Company: AIZ
Filing Date: 2025-08-15
Form Type: 424B5
Source: 0001193125-25-181851
Chunk: 1

Company: ASSURANT, INC.
Filing Date: 2025-08-15
Form: 424B5
Chunk 1
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     | 297,084,000 |

| (1) | Plus accrued interest, if any, from and including August 18, 2025, if settlement occurs after that date. |

The Notes are a new issue of securities for which there is currently no established public trading market. We do not intend to apply for listing of the Notes on any national securities exchange or for quotation of the Notes on any automated dealer quotation system. 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 S.A., and Euroclear Bank SA/NV, on or about August 18, 2025, against payment in immediately available funds. Joint Book-Running Managers

| Barclays |     | Goldman Sachs & Co. LLC |

| J.P. Morgan |     | KeyBanc Capital Markets |     | US Bancorp |     | Wells Fargo Securities |

Co-Managers

| BBVA |     | Citigroup |     | Lloyds Securities |     | Morgan Stanley |

The date of this prospectus supplement is August 14, 2025

This document consists of two parts. The first part is this prospectus supplement, which
describes the terms of this offering of the Notes and adds to and updates information contained or incorporated by reference in the accompanying prospectus. The second part, the accompanying prospectus, dated January 22, 2024, gives more
general information about us and our debt securities, some of which may not apply to this offering. To the extent any information varies between this prospectus supplement and the accompanying prospectus, you should rely on the information contained
in this prospectus supplement.

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