Company: ADP
Filing Date: 2025-05-07
Form Type: 424B2
Source: 0001193125-25-114878
Chunk: 35

Company: AUTOMATIC DATA PROCESSING INC
Filing Date: 2025-05-07
Form: 424B2
Chunk 35
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 the obligations of the underwriters to purchase the Notes included in this offering are subject to approval of legal matters by counsel and to other conditions. Subject to the terms and conditions set forth in the underwriting agreement, the underwriters have agreed, severally and not jointly, to purchase all of the notes sold under the underwriting agreement if any of these notes are purchased. If an underwriter defaults, the underwriting agreement provides that the purchase commitments of the non-defaultingunderwriters may be increased or the underwriting agreement may be terminated. Notes sold by the underwriters to the public will initially be offered at the initial public offering price set forth on the cover of this prospectus supplement. Any Notes sold by the underwriters to securities dealers may be sold at such initial public offering price less a concession not to exceed 0.25% of the principal amount of the Notes. The underwriters may allow, and such securities dealers may reallow, a concession not to exceed 0.15% of the principal amount of the Notes. If all the Notes are not sold at the initial offering price, the underwriters may change the offering price and the other selling terms. S-27

The following table shows the underwriting discounts that we are to pay to the underwriters in connection with this offering (expressed as a percentage of the principal amount of the Notes).

|          |     | Paid by the 
 Company     |       |   |
| Per Note |     |             | 0.400 | % |

We estimate that our total expenses for this offering, including costs related to interest rate hedges, will be approximately $6.1 million. In connection with the offering, the underwriters may purchase and sell the Notes in the open market. Purchases and sales in the open market may include short sales, purchases to cover short positions and stabilizing purchases.

| • |     | Short sales involve secondary market sales by the underwriters of a greater number of the Notes than they are 
 required to purchase in this offering.                                                                        |

| • |     | Covering transactions involve purchases of the Notes in the open market after the distribution has been completed 
 in order to cover short positions.                                                                                |

| • |     | Stabilizing transactions involve bids to purchase the Notes so long as the stabilizing bids do not exceed a 
 specified maximum.                                                                                          |

Purchases to cover short positions and stabilizing purchases, as well as other purchases by the underwriters for their own accounts, may have the effect of preventing or retarding