The information in this preliminary prospectus supplement and the accompanying prospectus is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not offers to sell these securities and we are not soliciting offers to buy these securities in any jurisdiction where the offer or sale is not permitted.

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-222648

SUBJECT TO COMPLETION, DATED MARCH 14, 2018

Prospectus Supplement

(to Prospectus dated January 22, 2018)

Assurant, Inc.

$                % Senior Notes due 2023    

$                % Senior Notes due 2028    

$                         % Fixed-to-Floating Rate Subordinated Notes due 2048    

We will pay interest on the     % senior notes due 2023 (the “2023 Senior Notes”), the     % senior notes due 2028 (the “2028 Senior Notes” and, together with the 2023 Senior Notes, the “Senior Notes”) on             and             of each year, beginning on             , 2018. The 2023 Senior Notes will mature on            , 2023 and the 2028 Senior Notes will mature on            , 2028.

Prior to            , 2023 (one month prior to maturity (the “2023 Senior Notes Par Call Date”)), we may redeem the 2023 Senior Notes, at any time in whole or from time to time in part, at a “make-whole” premium plus accrued and unpaid interest to, but excluding, the redemption date. Commencing on or after the 2023 Senior Notes Par Call Date, we may redeem the 2023 Senior Notes, at any time in whole or from time to time in part, at a redemption price equal to 100% of the principal amount of the 2023 Senior Notes being redeemed plus accrued and unpaid interest to, but excluding, the redemption date. Prior to            , 2028 (three months prior to maturity (the “2028 Senior Notes Par Call Date”)), we may redeem the 2028 Senior Notes, at any time in whole or from time to time in part, at a “make-whole” premium plus accrued and unpaid interest to, but excluding, the redemption date. Commencing on or after the 2028 Senior Notes Par Call Date, we may redeem the 2028 Senior Notes, at any time in whole or from time to time in part, at a redemption price equal to 100% of the principal amount of the 2028 Senior Notes being redeemed plus accrued and unpaid interest to, but excluding, the redemption date. See “Description of the Senior Notes—Optional Redemption.”

The Senior Notes will be our senior unsecured obligations and will rank equally with all of our other senior unsecured indebtedness from time to time outstanding and senior in right of payment to all existing and future subordinated indebtedness, including the Fixed-to-Floating Rate Subordinated Notes offered hereby (as defined herein).

The fixed-to-floating rate subordinated notes due 2048 (the “Fixed-to-Floating Rate Subordinated Notes” and, together with the Senior Notes, the “Notes”) will bear interest from            , 2018 to, but excluding,             , 2028, at an annual rate of                %, payable semi-annually in arrears on             and                of each year, beginning on            , 2018 and ending on            , 2028. From and including                 , 2028, the Fixed-to-Floating Rate Subordinated Notes will bear interest at an annual rate equal to three-month LIBOR plus                %, payable quarterly in arrears on     ,     ,     and    of each year, beginning on            , 2028. So long as no event of default with respect to the Fixed-to-Floating Rate Subordinated Notes has occurred and is continuing, we have the right, on one or more occasions, to defer the payment of interest on the Fixed-to-Floating Rate Subordinated Notes as described in this prospectus supplement for one or more consecutive interest periods for up to five years. Deferred interest will accrue additional interest at an annual rate equal to the annual interest rate then applicable to the Fixed-to-Floating Rate Subordinated Notes.

The principal amount of the Fixed-to-Floating Rate Subordinated Notes will mature on            , 2048. Payment of the principal on the Fixed-to-Floating Rate Subordinated Notes will be accelerated only in the case of a bankruptcy of or certain other insolvency events with respect to Assurant, Inc. There is no right of acceleration in the case of default in the payment of interest on the Fixed-to-Floating Rate Subordinated Notes or the performance of any of our other obligations with respect to the Fixed-to-Floating Rate Subordinated Notes.

We may redeem the Fixed-to-Floating Rate Subordinated Notes, in whole but not in part, at any time prior to             , 2028, within 90 days after the occurrence of a “rating agency event,” a “tax event” or a “regulatory capital event” at a redemption price equal to (i) with respect to a “rating agency event,” 102% of their principal

amount, and (ii) with respect to a “tax event” or a “regulatory capital event,” their principal amount, in each case plus accrued and unpaid interest (including compounded interest). On or after            , 2028, we may redeem the Fixed-to-Floating Rate Subordinated Notes, in whole at any time or in part from time to time, at a redemption price equal to their principal amount plus accrued and unpaid interest (including compounded interest) to, but excluding, the date of redemption; provided that if the Fixed-to-Floating Rate Subordinated Notes are not redeemed in whole, at least $25 million aggregate principal amount of the Fixed-to-Floating Rate Subordinated Notes, excluding any Fixed-to-Floating Rate Subordinated Notes held by us or any of our affiliates, must remain outstanding after giving effect to such redemption. For more information and the definitions of “tax event,” “rating agency event” and “regulatory capital event,” see “Description of the Fixed-to-Floating Rate Subordinated Notes—Redemption” in this prospectus supplement.

The Fixed-to-Floating Rate Subordinated Notes will be unsecured, will rank equally in right of payment to all our existing and future paripassu securities (as defined herein) and will be subordinated and junior in right of payment to all our existing and future senior indebtedness (as defined herein), including the Senior Notes offered hereby.

We intend to use the net proceeds of this offering, together with the net proceeds from the issuance of 2,875,000 shares of our 6.50% Series D Mandatory Convertible Preferred Stock (the “Mandatory Convertible Preferred Stock”), available cash on hand and common stock consideration, to finance our pending acquisition of TWG Holdings Limited (the “TWG Acquisition”), to refinance our 2018 Notes (as defined herein) and to pay related fees and expenses. See “Summary—Recent Developments” and “Use of Proceeds.” If the TWG Acquisition has not closed on or prior to December 17, 2018 or an Acquisition Termination Event (as defined herein) occurs, we will be required to redeem the 2023 Senior Notes and the Fixed-to-Floating Rate Subordinated Notes, in whole but not in part, at a redemption price equal to 101% of the aggregate principal amount of such notes, plus accrued and unpaid interest on such notes to the date of redemption. See “Description of the Senior Notes—Special Mandatory Redemption” and “Description of the Fixed-to-Floating Rate Subordinated Notes—Special Mandatory Redemption.”

The 2028 Senior Notes are not subject to the special mandatory redemption and will remain outstanding even if we do not consummate the TWG Acquisition.

The closing of this offering is not conditioned on the consummation of the TWG Acquisition, which, if consummated, will occur subsequent to the closing of this offering.

See “Risk Factors” on page S-13 of this prospectus supplement and page 4 of the accompanying prospectus to read about factors you should consider before investing in the Notes.

Neither the Securities and Exchange Commission (the “SEC”) nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the Notes to purchasers through the book-entry delivery system of The Depository Trust Company for the accounts of its participants, including Clearstream Banking, société anonyme, and Euroclear Bank S.A./N.V., on or about March    , 2018, against payment in immediately available funds.

Joint Book-Running Managers

US Bancorp    

The date of this prospectus supplement is             , 2018

This document consists of two parts. The first part is this prospectus supplement, which describes the terms of this offering of the Notes. The second part, the accompanying prospectus, dated January 22, 2018, gives more general information, some of which may not apply to this offering.

We and the underwriters have not authorized anyone to provide any information other than that contained in this prospectus supplement and the accompanying prospectus or incorporated by reference in this prospectus supplement and the accompanying prospectus or in any free writing prospectus prepared by or on behalf of us to which we have referred you. We and the underwriters take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We are not, and the underwriters are not, making an offer of the Notes in any jurisdiction where the offer is not permitted. You should not assume that the information contained in this prospectus supplement and the accompanying prospectus or incorporated by reference in this prospectus supplement and the accompanying prospectus is accurate as of any date other than the date of such document. Our business, financial condition, results of operations and prospects may have changed since those dates.

References in this prospectus supplement and the accompanying prospectus to “we,” “us,” “our” and the “Company” are to Assurant, Inc. and not its subsidiaries, except where the context otherwise requires.

Except as expressly indicated in this prospectus supplement, amounts in U.S. dollars represent whole dollar amounts, not thousands. This differs from the convention used in certain of the documents incorporated by reference herein.

TABLE OF CONTENTS

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INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows the Company to “incorporate by reference” the information it files with the SEC. This permits us to disclose important information to you by referencing these filed documents, which are considered part of this prospectus supplement and the accompanying prospectus. Information that we file later with the SEC will automatically update and supersede this information.

We incorporate by reference the documents set forth below that the Company previously filed with the SEC and any future filings made with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), until the offering of the Notes has been completed; provided that, unless otherwise stated, we will not incorporate by reference any filing that is “furnished” or deemed “furnished” to the SEC. These documents contain important information about the Company.

We will provide without charge, upon written or oral request, a copy of any or all of the documents that are incorporated by reference in this prospectus supplement and the accompanying prospectus. You may obtain these copies by writing to Investor Relations, Assurant, Inc., 28 Liberty Street, 41st Floor, New York, New York 10005 or by dialing (212)-859-7000. Our website is www.assurant.com. We make our periodic reports and other information filed or furnished to the SEC available, free of charge, through our website, as soon as reasonably practicable after those reports and other information are electronically filed with or furnished to the SEC. Except as specifically noted, information on our website and the websites of our operating companies is not incorporated by reference into this prospectus supplement and the accompanying prospectus and does not constitute a part of this prospectus supplement and the accompanying prospectus.

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RISK FACTORS

Investing in the Notes involves risks. In considering whether you should invest in the Notes, you should consider all of the information we have included or incorporated by reference in this prospectus supplement and the accompanying prospectus. In particular, you should carefully consider the risk factors described below, as well as in our Annual Report on Form 10-K for the year ended December 31, 2017 under “Item 1A. Risk Factors.” You should also read all other information contained in or incorporated by reference in this prospectus supplement and the accompanying prospectus before deciding to invest in the Notes. If any of the risks actually occur, they may materially harm our business, financial condition, operating results or cash flow. Additional risks and uncertainties that are not yet identified or that we think are immaterial may also materially harm our business, financial condition, operating results or cash flow and could result in a complete or partial loss of your investment.

This prospectus supplement, the accompanying prospectus and the incorporated documents also contain forward-looking statements that involve risks and uncertainties. Our actual results could differ materially from those anticipated in these forward-looking statements as a result of certain factors, including the risks faced by us as described in this prospectus supplement and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus. For more information see “Forward-Looking Information” in the accompanying prospectus and in this prospectus supplement.

We could incur significant additional indebtedness in the future, which could impair our ability to make payments under the Notes.

As of December 31, 2017, we had total outstanding indebtedness of approximately $1.07 billion, and no outstanding shares of preferred stock. On March 12, 2018 we completed the issuance of 2,875,000 shares of Mandatory Convertible Preferred Stock. On an as adjusted basis after giving effect to the TWG Acquisition, including the incurrence of indebtedness to partially fund the acquisition, we would have had approximately $2.01 billion of outstanding indebtedness and an additional $441 million of available borrowing under our revolving credit facility, all of which would be unsecured indebtedness. See “Capitalization” for more information. In addition, the Notes and the indentures governing the Notes generally do not contain restrictive covenants, such as a limitation on the payments of dividends (except in connection with an interest deferral on the Fixed-to-Floating Rate Subordinated Notes), the incurrence of indebtedness or the issuance or repurchase of securities by us. Thus, we may incur substantial additional indebtedness in the future, which could affect our ability to make payments under the Notes.

Holders of Notes have only limited rights of acceleration.

Holders of Notes may accelerate payment of the principal and accrued and unpaid interest on the Notes only upon the occurrence and continuation of an event of default. An event of default under the Senior Notes is generally limited to payment defaults, breaches of specific covenants and specific events of bankruptcy, insolvency and reorganization relating to us. Events of default under the Fixed-to-Floating Rate Subordinated Notes are even more limited. The Fixed-to-Floating Rate Subordinated Notes will be accelerated only in the case of a bankruptcy of or certain other insolvency events with respect to Assurant, Inc. There is no right of acceleration in the case of default in the payment of interest on the Fixed-to-Floating Rate Subordinated Notes or the performance of any of our other obligations with respect to the Fixed-to-Floating Rate Subordinated Notes.

If an active trading market does not develop for the Notes, you may not be able to resell your Notes.

There is no established trading market for the Notes. We cannot assure you that an active market for the Notes will develop or be sustained or that holders of the Notes will be able to sell their Notes at favorable prices or at all. Although the underwriters have indicated to us that they intend to make a market for the Notes, as permitted by applicable laws and regulations, they are not obligated to do so and may discontinue any such market-making at any time without notice. Accordingly, no assurance can be given as to the liquidity of, or

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trading markets for, the Notes. We do not intend to list the Notes on any securities exchange or include them on any automated quotation system. The liquidity of any market for the Notes will depend upon various factors, including:

In addition, the liquidity of the trading market for the Notes, and the market price quoted for the Notes, may be adversely affected by changes in the overall market for fixed income securities generally. As a result, an active trading market may not develop for the Notes. If no active trading market develops, you may not be able to resell your Notes at a price that reflects accrued and unpaid interest, if at all.

Failure to complete the TWG Acquisition could negatively affect our business and financial results.

If closing under the Amended and Restated Agreement and Plan of Merger, dated January 8, 2018 entered into in connection with the TWG Acquisition (the “TWG Agreement”) is not completed, we will be subject to a number of risks, including but not limited to the following:

Each of these factors may adversely affect our business and financial results. This offering is not conditioned upon the consummation of the TWG Acquisition. The 2023 Senior Notes and the Fixed-to-Floating Rate Subordinated Notes will be subject to a special mandatory redemption, and the 2028 Senior Notes are not subject to a special mandatory redemption. As a result, if closing under the TWG Agreement is not consummated, holders of the 2028 Senior Notes would be exposed to the risks described above and various other risks, including our inability to use the proceeds from this offering effectively.

The trading price of our Notes may be negatively affected if we are unable to integrate TWG effectively.

Strategic transactions like the TWG Acquisition create numerous uncertainties and risks and require significant effort and expenditures. We will need to effectively manage the integration of TWG and its personnel as well as changes in operations and systems. We may encounter unexpected difficulties or incur unexpected costs, including diversion of management’s attention to integration of operations and corporate and administrative infrastructures; difficulties in achieving anticipated business opportunities and growth prospects from combining the businesses of TWG with that of Assurant; difficulties in the integration of operations and systems; difficulties in the assimilation of employees and corporate cultures; and challenges in keeping existing customers and obtaining new customers.

The market price of the Notes may decline following the closing of the TWG Acquisition if the integration of TWG is unsuccessful, takes longer than expected or fails to achieve financial benefits to the extent anticipated by financial analysts or investors, or the effect of the business combination on the financial results of the combined company is otherwise not consistent with the expectations of financial analysts or investors.

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The unaudited pro forma condensed combined financial information included in this prospectus supplement is preliminary and our actual financial condition and results of operations after completing the TWG Acquisition may differ materially.

As of the date of this prospectus supplement the TWG Acquisition has not closed and we have not completed the detailed valuation analysis necessary to arrive at the required estimates of the fair value of TWG’s assets to be acquired and the liabilities to be assumed and the related allocations of purchase price, nor have we identified all adjustments necessary to conform TWG’s accounting policies to our accounting policies. A final determination of the fair value of TWG’s assets and liabilities, including intangible assets, will be based on the actual net tangible and intangible assets and liabilities of TWG as of the closing date of the TWG Acquisition.

As a result, the unaudited pro forma condensed combined financial information included in this prospectus supplement is preliminary and is provided for illustrative purposes only. It is not necessarily indicative of operating results and the financial position that would have been achieved had the TWG Acquisition occurred on the date assumed for purposes of that presentation and is subject to change as additional information becomes available and as additional analyses are performed. Furthermore, the unaudited pro forma condensed combined financial information does not purport to project the future operating results or financial position of the combined company following the TWG Acquisition. The adjustments applied to the historical financial information of TWG are based on estimates using historical information prepared by TWG’s management. The adjustments are based on estimates and assumptions that may not prove to be accurate which may cause variations in the final purchase accounting. Additionally, in connection with the final purchase accounting, additional differences in the accounting policies of Assurant and TWG may be identified, which could result in further variations from the pro forma financial information presented herein.

For more information, see “Unaudited Pro Forma Condensed Combined Financial Statements.”

In the event that the TWG Acquisition has not closed on or prior to December 17, 2018 or if an Acquisition Termination Event occurs, we will be required to redeem the 2023 Senior Notes and the Fixed-to-Floating Rate Subordinated Notes, in whole but not in part, at a redemption price equal to 101% of the aggregate principal amount of such notes, plus accrued and unpaid interest on such notes on the date of redemption, and, as a result, holders of such notes may not obtain their expected return on such notes.

We may not consummate the TWG Acquisition on or prior to December 17, 2018, or an Acquisition Termination Event may occur. Our ability to consummate the TWG Acquisition is subject to customary closing conditions, including regulatory approvals and other matters over which we have limited or no control. In the event that the TWG Acquisition has not closed on or prior to December 17, 2018, or an Acquisition Termination Event occurs, we will be required to redeem the 2023 Senior Notes and the Fixed-to-Floating Rate Subordinated Notes, in whole but not in part, at a redemption price equal to 101% of the aggregate principal amount or such notes, plus accrued and unpaid interest on such notes on the date of redemption. See “Description of the Senior Notes — Special Mandatory Redemption” and “Description of the Fixed-to-Floating Rate Subordinated Notes — Special Mandatory Redemption.” If we redeem the 2023 Senior Notes and the Fixed-to-Floating Rate Subordinated Notes pursuant to the special mandatory redemption, holders of such notes may not obtain their expected return on such notes. Your decision to invest in the 2023 Senior Notes or the Fixed-to-Floating Rate Subordinated Notes is made at the time of the offering of the notes. You will have no rights under the special mandatory redemption provision if the closing of the TWG Acquisition occurs on or before December 17, 2018, nor will you have any right to require us to redeem your 2023 Senior Notes or the Fixed-to-Floating Rate Subordinated Notes if, between the closing of the Notes offering and the closing of the TWG Acquisition, we experience any changes in our business or financial condition or if the terms of the TWG Acquisition change.

We are not obligated to place the proceeds from the sale of the Notes in escrow prior to the closing of the TWG Acquisition.

In the event that the TWG Acquisition has not closed on or prior to December 17, 2018, or an Acquisition Termination Event occurs, we will be required to redeem the 2023 Senior Notes and the Fixed-to-Floating Rate

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Subordinated Notes, in whole but not in part, at a redemption price equal to 101% of the aggregate principal amount of such notes, plus accrued and unpaid interest on such notes on the date of redemption. See “Description of the Senior Notes — Special Mandatory Redemption” and “Description of the Fixed-to-Floating Rate Subordinated Notes — Special Mandatory Redemption.” We are not obligated to place the net proceeds from the sale of the Notes in escrow prior to the closing of the TWG Acquisition or to provide a security interest in those proceeds, and there are no restrictions on our use of those proceeds during such time. Accordingly, we will need to fund any special mandatory redemption using cash on hand, net proceeds of this offering that we have voluntarily retained or from other sources of liquidity. We cannot assure you that we will have sufficient funds available when needed to make any required redemption of the 2023 Senior Notes and the Fixed-to-Floating Rate Subordinated Notes offered hereby. Any failure to redeem any of these 2023 Senior Notes and the Fixed-to-Floating Rate Subordinated Notes would constitute a default under the senior notes indenture and subordinated indenture governing the 2023 Senior Notes and the Fixed-to-Floating Rate Subordinated Notes, as applicable, offered hereby.

We have the right to defer interest for up to five consecutive years on the Fixed-to-Floating Rate Subordinated Notes.

We have the right at one or more times to defer payment of interest on the Fixed-to-Floating Rate Subordinated Notes for one or more consecutive interest periods for up to five years. During any such deferral period, holders of Fixed-to-Floating Rate Subordinated Notes will receive limited or no current payments on the Fixed-to-Floating Rate Subordinated Notes. Holders will have no remedies against us for nonpayment unless we fail to pay all deferred interest (including compounded interest) at the end of the five-year deferral period, at the maturity date or, if applicable, at any earlier accelerated maturity date arising from an event of default or any earlier redemption date.

Deferral of interest payments and other characteristics of the Fixed-to-Floating Rate Subordinated Notes could adversely affect the market price of the Fixed-to-Floating Rate Subordinated Notes.

To the extent a secondary market develops for the Fixed-to-Floating Rate Subordinated Notes, the market price of the Fixed-to-Floating Rate Subordinated Notes is likely to be adversely affected if we defer payments of interest on the Fixed-to-Floating Rate Subordinated Notes. As a result of our deferral right or if investors perceive that there is a likelihood that we will exercise our deferral right, the market for the Fixed-to-Floating Rate Subordinated Notes may become less active or be discontinued during such a deferral period, and the market price of the Fixed-to-Floating Rate Subordinated Notes may be more volatile than the market prices of other securities that are not subject to deferral. If we do defer interest on the Fixed-to-Floating Rate Subordinated Notes and you sell your Fixed-to-Floating Rate Subordinated Notes during the period of that deferral, you may not receive the same return on your investment as a holder that continues to hold its Fixed-to-Floating Rate Subordinated Notes until we pay the deferred interest at the end of the applicable deferral period.

If interest payments on the Fixed-to-Floating Rate Subordinated Notes are deferred, holders of the Fixed-to-Floating Rate Subordinated Notes will be required to recognize income for U.S. federal income tax purposes in advance of the receipt of cash attributable to such income.

If we defer interest payments on the Fixed-to-Floating Rate Subordinated Notes, the Fixed-to-Floating Rate Subordinated Notes would be treated as issued with original issue discount (“OID”) at the time of such deferral, and all stated interest due after such deferral would be treated as OID. In such case, a U.S. Holder (as defined in this prospectus supplement under “Certain U.S. Federal Income Tax Considerations”) would be required to include such stated interest in income as it accrued, regardless of its regular method of tax accounting, using a constant yield method, before such holder receives any payment attributable to such income, and would not separately report the actual cash payments of interest on the Fixed-to-Floating Rate Subordinated Notes as taxable income. See “Certain U.S. Federal Income Tax Considerations – Taxation of the Fixed-to-Floating Rate Subordinated Notes.”

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The subordinated indenture does not limit the amount of senior or pari passu indebtedness we may issue, and other future liabilities may rank senior to or equally with the Fixed-to-Floating Rate Subordinated Notes in right of payment or upon liquidation.

The Fixed-to-Floating Rate Subordinated Notes will be subordinate and junior in right of payment to our current and future senior indebtedness, including the Senior Notes offered hereby, which means we cannot make any payments on the Fixed-to-Floating Rate Subordinated Notes if we are in default on any of our indebtedness that is senior to the Fixed-to-Floating Rate Subordinated Notes. Therefore, in the event of our bankruptcy, liquidation or dissolution, our assets must be used to pay off our senior indebtedness in full before any payment may be made on the Fixed-to-Floating Rate Subordinated Notes.

Our senior indebtedness includes all of our obligations for amounts borrowed (other than the Fixed-to-Floating Rate Subordinated Notes and other obligations issued under the subordinated indenture), as well as other obligations such as capital leases, but will not include (1) obligations to trade creditors created or assumed by us in the ordinary course of business or (2) indebtedness that is by its terms subordinate, or not superior, in right of payment to the Fixed-to-Floating Rate Subordinated Notes, including our pari passu securities. All of our existing indebtedness for amounts borrowed, other than our pari passu securities, is senior indebtedness. In addition, the Notes will be effectively subordinated to all existing and future liabilities of our subsidiaries to the extent of the assets of such subsidiaries, including future policy benefits and expenses, claims and benefits payable and separate account balances of $16.02 billion as of December 31, 2017.

The terms of the subordinated indenture do not limit our or our subsidiaries’ ability to incur additional debt, whether secured or unsecured, and including indebtedness that ranks senior to or pari passu with the Fixed-to-Floating Rate Subordinated Notes upon our liquidation or in right of payment as to principal or interest.

We may make payments on senior securities and certain payments on pari passu securities during a deferral period.

The terms of the Fixed-to-Floating Rate Subordinated Notes and the subordinated indenture do not restrict our ability to make any payment on senior securities during a deferral period. In addition, the terms of the Fixed-to-Floating Rate Subordinated Notes and the subordinated indenture permit us to make any payment of current or deferred interest on pari passu securities so long as the amounts paid, the amounts set aside at such time for payment of such pari passu securities on the immediately following regularly scheduled interest payment dates therefor and the amounts paid or set aside at such time for payment on the Fixed-to-Floating Rate Subordinated Notes on the immediately following interest payment date for the Fixed-to-Floating Rate Subordinated Notes, are in the same proportion to the full payment to which each series of such pari passu securities and the Fixed-to-Floating Rate Subordinated Notes is then, or on such immediately following regularly scheduled interest payment dates will be, entitled to be paid in full.

We may redeem the Fixed-to-Floating Rate Subordinated Notes on or after                , 2028, and at any time in the event of a tax event, rating agency event or regulatory capital event.

We may redeem the Fixed-to-Floating Rate Subordinated Notes, in whole at any time or in part from time to time, on or after                , 2028 at a redemption price equal to their principal amount plus accrued and unpaid interest (including compounded interest) to, but excluding, the date of redemption; provided that if the Fixed-to-Floating Rate Subordinated Notes are not redeemed in whole, at least $25 million aggregate principal amount of the Fixed-to-Floating Rate Subordinated Notes, excluding any Fixed-to-Floating Rate Subordinated Notes held by us or any of our affiliates, must remain outstanding after giving effect to such redemption. Prior to                , 2028, we may also redeem the Fixed-to-Floating Rate Subordinated Notes in whole, but not in part, at any time within 90 days after the occurrence of a “rating agency event,” a “tax event” or a “regulatory capital event” (each as defined herein) at a redemption price equal to (i) with respect to a “rating agency event,” 102% of their principal amount, and (ii) with respect to a “tax event” or a “regulatory capital event,” their principal amount, in each case, plus accrued and unpaid interest (including compounded interest) to, but excluding, the date of redemption.

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Events that would constitute a “rating agency event,” a “tax event” or a “regulatory capital event” could occur at any time and could result in the Fixed-to-Floating Rate Subordinated Notes being redeemed earlier than would otherwise be the case. In the event we choose to redeem the Fixed-to-Floating Rate Subordinated Notes, you may not be able to reinvest the redemption proceeds in a comparable security at an effective interest rate as high as the interest rate on the Fixed-to-Floating Rate Subordinated Notes. For more information and the definitions of “tax event,” “rating agency event” and “regulatory capital event,” see “Description of the Fixed-to-Floating Rate Subordinated Notes—Optional Redemption” in this prospectus supplement.

Under an amendment to section 163(j) of the Internal Revenue Code of 1986, as amended, that took effect on January 1, 2018, limitations on our ability to deduct interest expense on the Fixed-to-Floating Rate Subordinated Notes may apply if our interest expense deductions exceed 30 percent of our adjusted taxable income. Regulations or other guidance from the Internal Revenue Service (the “IRS”) may be issued addressing the application of section 163(j), which guidance may affect our ability to deduct interest expense on the Fixed-to-Floating Rate Subordinated Notes. Any guidance of this kind will not constitute a tax event, unless the guidance limits, defers or prohibits the deduction of interest on the Fixed-to-Floating Rate Subordinated Notes in a manner or to an extent different from and more adverse than interest on our senior debt by reason of the specific characteristics of the Fixed-to-Floating Rate Subordinated Notes.

Increased regulatory oversight, uncertainty relating to the LIBOR calculation process and potential discontinuation or reform of LIBOR may adversely affect the value of and return on your Fixed-to-Floating Rate Subordinated Notes.

From and including                 , 2028 to, but excluding, the maturity date or any earlier redemption date, the Fixed-to-Floating Rate Subordinated Notes will bear interest at interest rates based on the London Interbank Offered Rate (for purposes of this risk factor, “LIBOR”). LIBOR is deemed to be a “benchmark” and is the subject of ongoing national and international regulatory scrutiny and reform. Some of these reforms are already effective, while others are still to be implemented or formulated. For example, in July 2017, the United Kingdom Financial Conduct Authority, which regulates LIBOR, announced that it intends to stop persuading or compelling banks to submit rates for the calculation of LIBOR to the administrator of LIBOR after 2021. The announcement indicates that the continuation of LIBOR on the current basis cannot and will not be guaranteed after 2021. Uncertainty as to the nature of potential changes to LIBOR, alternative reference rates or other reforms may cause such “benchmarks” to perform differently than they performed in the past or to be discontinued entirely and may have other consequences that cannot be predicted. Any such consequences could adversely affect the value of and return on your Fixed-to-Floating Rate Subordinated Notes and the trading market for the Fixed-to-Floating Rate Subordinated Notes.

To the extent that the Fixed-to-Floating Rate Subordinated Notes bear interest at interest rates determined by reference to LIBOR and LIBOR is discontinued or is no longer quoted, interest due on the Fixed-to-Floating Rate Subordinated Notes during any floating-rate interest period (as defined below) will be determined using the alternative methods described in the definition of “three-month LIBOR” in this prospectus supplement under the caption “Description of the Fixed-to-Floating Rate Subordinated Notes—Interest rate and interest payment dates—Floating-rate period.” If the calculation agent determines that LIBOR has been discontinued, the calculation agent will determine whether to use a substitute or successor base rate that it has determined in its sole discretion is most comparable to three-month LIBOR, provided that if the calculation agent determines there is an industry accepted successor base rate, the calculation agent shall use such successor base rate. The calculation agent in its sole discretion may also implement changes to the business day convention, any business day definition, the interest determination date and any method for obtaining the substitute or successor base rate if such rate is unavailable on the relevant business day, in a manner that is consistent with industry accepted practices for such substitute or successor base rate. If this occurs, the value of the Fixed-to-Floating Rate Subordinated Notes, the return on the Fixed-to-Floating Rate Subordinated Notes and the trading market for the Fixed-to-Floating Rate Subordinated Notes may be adversely affected. The calculation agent has not been appointed and we will appoint a calculation agent prior to the commencement of the first floating-rate interest period.

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FORWARD-LOOKING STATEMENTS

Some of the statements included in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus, particularly those anticipating the TWG Acquisition, the benefits and synergies of the TWG Acquisition, including operating synergies, future opportunities for Assurant and any statements regarding Assurant’s financing plans, the combined company’s future results, financial condition and operations, the impact of recently enacted U.S. tax reform legislation, anticipated business levels and offerings, planned activities, anticipated growth, market presence and opportunities, strategies, competition and other expectations, targets and financial metrics for future periods, are forward-looking statements within the meaning of the U.S. Private Securities Litigation Reform Act of 1995. You can identify these statements by the fact that they may use words such as “will,” “may,” “anticipates,” “expects,” “estimates,” “projects,” “intends,” “plans,” “believes,” “targets,” “forecasts,” “potential,” “approximately” or the negative versions of those words and terms with a similar meaning. Any forward-looking statements contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference in this prospectus supplement and the prospectus are based upon our historical performance and on current plans, estimates and expectations. The inclusion of this forward-looking information should not be regarded as a representation by us or any other person that the future plans, estimates or expectations contemplated by us will be achieved. Our actual results might differ materially from those indicated in this prospectus supplement and the accompanying prospectus and the documents incorporated by reference in this prospectus supplement. We believe that these factors include but are not limited to those described under the section entitled “Risk Factors” in this prospectus supplement and under the sections entitled “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in our Annual Report on Form 10-K for the year ended December 31, 2017. These factors should not be construed as exhaustive and should be read in conjunction with the other cautionary statements that are included in this prospectus supplement and the accompanying prospectus and the documents incorporated by reference in this prospectus supplement. We undertake no obligation to update any forward-looking statements in this prospectus supplement or the accompanying prospectus or in the documents incorporated by reference in this prospectus supplement as a result of new information or future events or developments.

The following factors could cause our actual results to differ materially from those currently estimated by management:

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For a more detailed discussion of the risks that could affect our actual results, please refer to the risk factors identified in our SEC reports, including, but not limited to, our Annual Reports on Form 10-K and our Quarterly Reports on Form 10-Q, as filed with the SEC.

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USE OF PROCEEDS

We estimate that the net proceeds from this offering will be approximately $                 million after deducting underwriting discounts and commissions and the estimated offering expenses payable by us. We intend to use the net proceeds of this offering, together with the net proceeds from the March 12, 2018 issuance of 2,875,000 shares of the Mandatory Convertible Preferred Stock, available cash on hand and common stock consideration, to finance the TWG Acquisition, refinance our 2018 Notes and pay related fees and expenses.

The following table outlines the sources and uses of funds for the TWG Acquisition, the refinancing of our 2018 Notes and the payment of related fees and expenses. The table assumes that the TWG Acquisition, the issuance of 2,875,000 shares of the Mandatory Convertible Preferred Stock, the common stock issued as consideration in the TWG acquisition, the refinancing of our 2018 Notes and this offering are completed simultaneously, although this offering is expected to close prior to the consummation of the TWG Acquisition, including the issuance of the common stock consideration. The amounts in this table differ from the assumptions in the Summary Unaudited Pro Forma Condensed Combined Financial information included herein due to changes in amounts issued in connection with the Mandatory Convertible Preferred Stock issuance (to reflect the issuance of the Option Shares (as defined below)), changes in the Assurant common stock price to March 9, 2018, a change in assumption regarding the amount of new indebtedness to be issued, as well as resultant available cash on hand expected to be utilized.

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RATIO OF EARNINGS TO FIXED CHARGES

The following table presents (1) our historical ratio of earnings to fixed charges for the periods indicated, (2) the adjusted ratio of earnings to fixed charges for the year ended December 31, 2017, after giving effect to the $1.3 billion aggregate principal amount of Notes offered hereby as if it had been consummated as of the beginning of such period and (3) the as further adjusted ratio of earnings to combined fixed charges and preferred stock dividends for the year ended December 31, 2017, after giving effect to the TWG Acquisition and the refinancing of our 2018 Notes, the March 12, 2018 issuance of 2,875,000 shares of the Mandatory Convertible Preferred Stock, the issuance of $1.3 billion aggregate principal amount of Notes offered hereby and the common stock consideration in connection with the TWG Acquisition, in each case as if they had been consummated as of the beginning of such period:

Earnings represent:

Fixed charges include:

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CAPITALIZATION

The following table sets forth our consolidated capitalization at December 31, 2017:

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UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS

The following unaudited pro forma condensed combined financial statements are based on the separate historical financial statements of Assurant, Inc. (“Assurant” or the “Company”) and TWG Holdings Limited (“TWG”) after giving effect to the acquisition of TWG by Assurant and the exchange of Assurant’s outstanding common shares and other cash consideration for TWG ordinary shares in connection therewith, and the assumptions and adjustments described in the accompanying notes to the unaudited pro forma condensed combined financial statements. The unaudited pro forma condensed combined balance sheet as of December 31, 2017 is presented as if the Merger (as defined herein) had occurred on December 31, 2017. The unaudited pro forma condensed combined income statement for the year ended December 31, 2017 is presented as if the Merger had occurred on January 1, 2017. The historical condensed combined financial information has been adjusted to reflect factually supportable items that are directly attributable to the Merger and, with respect to the pro forma condensed combined income statements only, expected to have a continuing impact on the combined results of operations. However, and as further described below, the resulting pro forma condensed combined financial statements do not include any adjustments related to cost savings, operating synergies, tax benefits or revenue enhancements (or the necessary costs to achieve such benefits) that are expected to result from the Merger.

The preparation of the unaudited pro forma condensed combined financial statements and related adjustments required management to make certain assumptions and estimates. The unaudited pro forma condensed combined financial statements should be read together with:

The information presented below has been prepared based on the original assumed issuance of $1.35 billion aggregate principal amount of new indebtedness, the original planned issuance of $250 million of Mandatory Convertible Preferred Stock and Assurant, Inc.’s share price data as of March 2, 2018. These assumptions differ from those made elsewhere in this prospectus supplement, including in the sections “Use of Proceeds,” “Ratio of Earnings to Fixed Charges” and “Capitalization.” Specifically, the pro forma amounts differ from the assumptions in these sections due to subsequent changes in amounts issued in connection with the Mandatory Convertible Preferred Stock issuance (to reflect the issuance of the Option Shares), changes in the Assurant common stock price to March 9, 2018 (from March 2, 2018), a change in assumption regarding the amount of new indebtedness to be issued, as well as available cash on hand expected to be utilized. Management deemed such differences as not material for purposes of updating these pro forma condensed combined financial statements.

The unaudited pro forma condensed combined financial information has been prepared using the acquisition method of accounting for business combinations under accounting principles generally accepted in the United States of America (U.S. GAAP). Accordingly, the assets, liabilities and commitments of TWG, the acquiree, are adjusted to their estimated fair values on the assumed acquisition date of December 31, 2017. The estimates of fair value are preliminary and are dependent upon certain valuations that have not progressed to a stage where there is sufficient information to make a definitive valuation. The unaudited pro forma adjustments, including the allocations of the acquisition consideration, have been made solely for the purpose of providing unaudited pro forma condensed combined financial information. The unaudited pro forma adjustments are preliminary based upon available information and certain assumptions described in the accompanying notes to the unaudited pro forma condensed combined financial statements.

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A final determination of the acquisition consideration and fair values of TWG’s assets and liabilities will be based on the actual net tangible and intangible assets of TWG that exist as of the date of completion of the transaction. Consequently, amounts preliminarily allocated to the assets and liabilities, including goodwill and intangible assets could change significantly from those allocations used in the unaudited pro forma condensed combined financial statements presented below and could also result in a material change in amortization of acquired intangible assets. The unaudited pro forma condensed combined financial statements have been prepared by Assurant management in accordance with Article 11 of Regulation S-X promulgated by the SEC. The pro forma adjustments are based on estimates using information available at this time and therefore are preliminary and subject to change. There can be no assurance that such changes will not be material. The pro forma condensed combined financial information are not necessarily indicative of the combined financial position or results of operations that might have been achieved had the transaction been completed as of the dates indicated, nor are they meant to be indicative of any anticipated combined financial position or future results of operations that the combined company will experience after the transaction. The unaudited pro forma condensed combined financial statements also do not reflect any cost savings, operating synergies, tax benefits or revenue enhancements that the combined company may achieve as a result of the Merger, the costs to integrate the operations of Assurant or TWG, or the costs necessary to achieve such cost savings, operating synergies, tax benefits and revenue enhancements.

Article 11 requires that the income tax effects of pro forma adjustments be calculated based on the statutory rate in effect during the periods for which the pro forma income statement is being presented. For purposes of these condensed combined pro forma financial statements, we utilized the 35% statutory tax rate in effect for 2017 for the U.S. operations, and other applicable rates for the TWG international operations. As the U.S. Tax Cuts And Jobs Act was enacted in December 2017, all U.S. based deferred tax assets and liabilities established in connection with purchase accounting and other pro forma adjustments as of December 31, 2017 were determined utilizing the 21% U.S. statutory rate for 2018 and beyond (representing the periods when such deferred taxes will reverse).

Certain financial information of TWG, as presented in its historical consolidated financial statements, has been reclassified to conform to the historical presentation in Assurant’s consolidated financial statements, for purposes of preparing the unaudited pro forma condensed combined financial statements. Refer to Note 3 – TWG reclassification adjustments for an explanation of these reclassifications.

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Unaudited Pro Forma Condensed Combined Balance Sheet

As of December 31, 2017

(unaudited)

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1 – Historical TWG financial statement amounts after conforming reclassification adjustments. Refer to Note 3 – TWG reclassification adjustments.

(5a) to (5n)—refer to Note 5—Unaudited pro forma condensed combined balance sheet adjustments.

(7a) to (7d)—refer to Note 7—Financing adjustments for unaudited pro forma condensed combined balance sheet and statements of operations.

See accompanying notes to the unaudited pro forma condensed combined financial statements.

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Unaudited Pro Forma Condensed Combined Statement of Operations

For the Year Ended December 31, 2017

(unaudited)

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(6a) to (6f) – refer to Note 6—Unaudited pro forma condensed combined statements of operations adjustments.

(7e) to (7g)—refer to Note 7—Financing adjustments for unaudited pro forma condensed combined financial statements.

See accompanying notes to the unaudited pro forma condensed combined financial statements.

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NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS

1. Basis of Pro Forma Presentation

On January 8, 2018, the Company entered into an Amended and Restated Agreement and Plan of Merger (the “A&R Merger Agreement”), with TWG Holdings Limited, a Bermuda limited company (“TWG Holdings,” and together with its subsidiaries, “TWG”), TWG Re, Ltd., a corporation incorporated in the Cayman Islands (“TWG Re”), Arbor Merger Sub, Inc., a Delaware corporation and a direct wholly owned subsidiary of TWG Holdings (“TWG Merger Sub”) and Spartan Merger Sub, Ltd., a Bermuda exempted limited company and a direct wholly owned subsidiary of Assurant (“Merger Sub”). The A&R Merger Agreement amends and restates in its entirety that certain Agreement and Plan of Merger entered into by the Company, TWG, TWG Re and TWG Merger Sub on October 17, 2017 (the “Original Merger Agreement”). Under the terms of the A&R Merger Agreement and subject to the satisfaction or waiver of the conditions therein, in lieu of the transactions contemplated by the Original Merger Agreement, Assurant will acquire TWG through a transaction in which Merger Sub will merge with and into TWG, with TWG continuing as the surviving corporation and as a wholly owned subsidiary of Assurant (the “Merger”). TWG is a global provider of protection plans and related programs and a portfolio company of TPG Capital, a private equity company.

As a result of the proposed acquisition, the equityholders of TWG will receive consideration of 10,400,000 shares of Assurant common stock, which represents approximately 19.8% of Assurant’s currently outstanding shares of common stock, and cash. The cash consideration is subject to a collar mechanism based on the change between Assurant’s 10-day volume weighted average stock price at the time of closing (the “closing price”) and $95.4762, the reference price as set forth in the A&R Merger Agreement. Pursuant to the collar mechanism, the cash consideration may increase or decrease by the value of the difference between the closing price and the reference price if the percentage change is no more than 10% (in either direction). There is no further adjustment to the cash consideration if the percentage change between the two prices is within 10% to 20% (in either direction). In the event that the percentage change is greater than 20% (in either direction), the disadvantaged party may terminate the agreement unless the other party elects to cure by adjusting the consideration to be received by the TWG Holdings equityholders. Assuming an increase or decrease with respect to the reference price of not more than 10%, the total cash consideration would range from approximately $800.0 million to $1.0 billion, depending on Assurant’s stock price at closing.

The Company currently expects to finance the cash consideration and repayment of $590.2 million of TWG’s existing debt through a combination of external financing and available cash at the holding company at the time of close. Refer to Note 16 to the Assurant consolidated financial statements included in Assurant’s Annual Report on Form 10-K for the year ended December 31, 2017 for more information related to debt agreements.

The transaction is expected to close in the second quarter of 2018, subject to the receipt of regulatory approvals and other customary closing conditions.

The unaudited pro forma condensed combined balance sheet as of December 31, 2017 is presented as if the Merger with TWG had occurred on December 31, 2017 and the unaudited pro forma condensed combined statements of operations for the year ended December 31, 2017 is presented as if the Merger had occurred on January 1, 2017 (and are based on the historical financial statements of Assurant and TWG after giving effect to the completion of the Merger and the assumptions and adjustments described in the accompanying notes). Such pro forma adjustments are (1) factually supportable, (2) directly attributable to the Merger, and (3) with respect to the unaudited pro forma condensed combined statements of operations expected to have a continuing impact on the results of operations of the combined company.

The transaction will be accounted for under the acquisition method of accounting. In business combination transactions in which the consideration given is not in the form of cash, measurement of the acquisition consideration is based on the fair value of the consideration given or the fair value of the assets (or net assets) acquired, whichever is more clearly evident and, thus, more reliably measurable.

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All of the TWG assets acquired and liabilities assumed in this business combination will be recognized at their acquisition-date fair value, while transaction costs and integration costs associated with the business combination are expensed as incurred. The excess of the acquisition consideration over the fair value of assets acquired and liabilities assumed, if any, is allocated to goodwill. TWG existing goodwill, acquisition related intangible assets and deferred taxes will be eliminated and replaced by newly established amounts in connection with this business combination. Changes in deferred tax asset valuation allowances and income tax uncertainties, if any, after the acquisition date will generally affect income tax expense. Subsequent to the completion of the Merger, Assurant and TWG will finalize an integration plan, which may affect how the assets acquired, including intangible assets, will be utilized by the combined company.

Upon consummation of the Merger and the completion of a valuation, the acquisition consideration as well as estimated fair value of the assets and liabilities will be updated, including the estimated fair value and useful lives of the identifiable intangible assets, the acquisition consideration and allocation of the excess purchase price to goodwill.

The unaudited pro forma condensed combined financial information is presented solely for informational purposes and is not necessarily indicative of the combined results of operations or financial position that might have been achieved for the periods or dates indicated, nor is it necessarily indicative of the future results of the combined company.

2. Accounting Policies

As part of preparing the unaudited pro forma condensed combined financial statements, Assurant conducted a review of the accounting policies of TWG to determine if differences in accounting policies require pro forma adjustments to conform to Assurant’s accounting policies.

The pro forma condensed combined financial statements have been adjusted to conform to Assurant’s accounting for certain revenues. Specifically, TWG’s historical accounting for a portion of their revenues is presented net of certain costs paid by the consumer to the selling dealer or retailer acting as TWG’s agent as compared to Assurant’s accounting, which generally recognizes revenues for such contracts based on the actual amount paid by the consumer. Assurant’s accounting is based on the nature of the insurance products distributed to the end consumer, the role of wholly-owned insurance entities insuring the obligations as primary obligor, as well as consideration of the performance obligations and transaction prices specified within each contract. The difference in recording increased revenues and costs, and the related effect on assets and liabilities, does not affect net income. The conforming adjustments are reflected in the Value of business acquired and Unearned premiums and contract fees in the pro forma condensed combined balance sheet and in Net earned premiums and Amortization of deferred acquisition costs, value of business acquired and intangible assets in the pro forma combined statement of operations.

Upon consummation of the Merger, a more comprehensive review of the accounting policies of TWG will be performed, which may identify other differences among the accounting policies of Assurant and TWG that, when conformed, could have a material impact on the unaudited pro forma condensed combined financial statements.

3. TWG Reclassification Adjustments

Financial information of TWG in the “Historical TWG as of December 31, 2017 (after reclassification)” column of the unaudited pro forma condensed combined financial statements represents the historical reported balances of TWG reclassified to conform to the presentation in Assurant’s financial statements. Unless otherwise indicated, defined line items included in the notes to these pro forma financial statements have the meanings given to them in the historical financial statements of TWG.

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Reclassification and classification of the unaudited pro forma balance sheet as of December 31, 2017

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