Company: WBS-PG
Filing Date: 2025-09-05
Form Type: 424B5
Source: 0001193125-25-197211
Chunk: 6

Company: WEBSTER FINANCIAL CORP
Filing Date: 2025-09-05
Form: 424B5
Chunk 6
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 inquiries, the results of regulatory examinations or reviews, disruptions at regulatory agencies, government funding or other issues; |

| • |     | our ability to navigate differing environmental, social, governmental and sustainability concerns among federal                                  
 and state governmental administrations and judicial decisions, our stakeholders and other activists that may arise from our business activities; |

| • |     | our ability to assess and monitor the effect of evolving uses of artificial intelligence on our business and 
 operations;                                                                                                  |

| • |     | the occurrence of natural disasters, severe weather events, and public health crises, and any governmental or 
 societal responses thereto; and                                                                               |

| • |     | the impact of any of the foregoing on the business or credit quality of our customers. |

All forward looking statements attributable to our Company are expressly qualified in their entirety by these cautionary statements and we claim the protection of the safe harbor for forward looking statements contained in v

the Private Securities Litigation Reform Act of 1995 in connection with any such statement. We do not undertake any obligation to update or otherwise revise any forward-looking statements,
whether as a result of new information, future events or otherwise, except as required by federal securities laws. As forward-looking statements involve significant risks and uncertainties, caution should be exercised against placing undue reliance
on such statements. There is no assurance that future results, levels of activity, performance or goals will be achieved.

For additional
information that you should consider carefully in evaluating these forward-looking statements, see the section entitled “Risk Factors” on page S-6 of this prospectus supplement as well as the factors set forth under the “Risk
Factors” section in the accompanying prospectus and in any other documents incorporated or deemed to be incorporated by reference therein or herein, including our Annual Report on Form 10-Kfor the year ended December31, 2024,our Quarterly Report on Form 10-Qfor the quarter ended March31, 2025 and our Quarterly Report on Form 10-Qfor the quarter ended June30, 2025, as such discussion may be amended or updated by other reports filed by us with the SEC.

vi

PROSPECTUS SUPPLEMENT SUMMARY

This summary highlights selected information from this prospectus supplement and does not contain all of the information that you should consider in making your investment decision. You should read this summary together with the more detailed information appearing elsewhere in this prospectus supplement, as well as the information in the accompanying prospectus and in the documents incorporated by reference or deemed incorporated by reference into this