Company: AIZ
Filing Date: 2025-08-15
Form Type: 424B5
Source: 0001193125-25-181851
Chunk: 2

Company: ASSURANT, INC.
Filing Date: 2025-08-15
Form: 424B5
Chunk 2
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 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, or in any free
writing 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,” the
“Company” and “Assurant” 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.

It is important for you to read and
consider all information contained in this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference herein and therein, in making your investment decision. You should also read and consider the
information in the documents to which we have referred you in the sections entitled “Incorporation of Certain Documents by Reference” in this prospectus supplement and “Where You Can Find More Information” in the accompanying
prospectus.

TABLE OF CONTENTS Page Prospectus Supplement

| Incorporation of Certain Documents by Reference |     | S-ii |
| Summary                                         |     | S-1  |
| Forward-Looking Statements                      |     | S-5  |
| Risk Factors                                    |     | S-7  |
| Use of Proceeds                                 |     | S-9  |
| Capitalization                                  |     | S-10 |
| Description of the Notes                        |     | S-11 |
| Material U.S. Federal Income Tax Consequences   |     | S-15 |
| Certain Benefit Plan Considerations             |     | S-19 |
| Underwriting                                    |     | S-21 |
| Validity of the Notes                           |     | S-27 |
| Experts                                         |     | S-27 |

Prospectus

|                                                                                   |     | Page |     |
| About This Prospectus                                                             |     |      |  ii |
| Forward-Looking Information                                                       |     |      | iii |
| About Assurant, Inc.                                                              |     |      |   1 |
| Where You Can Find More Information