Company: ADP
Filing Date: 2025-05-07
Form Type: 424B2
Source: 0001193125-25-114878
Chunk: 0

Company: AUTOMATIC DATA PROCESSING INC
Filing Date: 2025-05-07
Form: 424B2
Chunk 0
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Filed Pursuant to Rule 424(b)(2)
Registration No. 333-281920 Prospectus Supplement (To Prospectus Dated September 4, 2024) $1,000,000,000 Automatic Data Processing, Inc. $1,000,000,000 4.750% Senior Notes due 2032 We are offering $1,000,000,000 of our 4.750% Senior Notes due 2032 (the “Notes”). We will pay interest on the Notes on May 8 and November 8 of each year, beginning on November 8, 2025. The Notes will mature on May 8, 2032. At our option, we may redeem the Notes offered hereby in whole or in part at any time and from time to time before their maturity date at the redemption prices described herein under “Description of Notes—Optional Redemption.” Upon a Change of Control Triggering Event, we will be required to make an offer to repurchase all outstanding Notes at a price in cash equal to 101% of the principal amount of the Notes, plus any accrued and unpaid interest to, but not including, the repurchase date. The Notes will be our direct, senior unsecured obligations and will rank equally with all of our other direct, senior unsecured indebtedness from time to time outstanding. Investing in the Notes involves risks. See the sections entitled “ Risk Factors” beginning on page S-6of this prospectus supplement and in our Annual Report on Form 10-Kfor the year ended June 30, 2024, which is incorporated by reference into this prospectus supplement and the accompanying prospectus.

|                                                              |     | Per Share |        |   |     | Total |             |
|:-------------------------------------------------------------|:----|:----------|-------:|:--|:----|:------|------------:|
| Public offering price(1)                                     |     |           | 99.841 | % |     | $     | 998,410,000 |
| Underwriting discounts                                       |     |           |  0.400 | % |     | $     |   4,000,000 |
| Proceeds to the Company (before expenses and commissions)(1) |     |           | 99.441 | % |     | $     | 994,410,000 |

| (1) | Plus accrued interest, if any, from May 8, 2025, if settlement occurs after that date. |