Company: ADP
Filing Date: 2025-09-25
Form Type: DEFA14A
Source: 0001308179-25-000608
Chunk: 0

Company: AUTOMATIC DATA PROCESSING INC
Filing Date: 2025-09-25
Form: DEFA14A
Chunk 0
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UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the
Securities Exchange Act of 1934 (Amendment No. )

| ☑ | Filed by the Registrant | ☐ | Filed by a party other 
 than the Registrant    |

| CHECK THE APPROPRIATE BOX: |     |                                              |
| ☐                          |     | Preliminary Proxy Statement                  |
| ☐                          |     | Confidential, for Use of the Commission Only 
 (as permitted by Rule 14a-6(e)(2))           |
| ☐                          |     | Definitive Proxy Statement                   |
| ☑                          |     | Definitive Additional Materials              |
| ☐                          |     | Soliciting Material under §240.14a-12        |

Automatic Data Processing, Inc. (Name of Registrant as Specified In Its Charter) (Name of Person(s) Filing Proxy Statement, if other than the Registrant)

| PAYMENT OF FILING FEE (CHECK ALL BOXES THAT APPLY): |     |                                                                                                     |
| ☑                                                   |     | No fee required                                                                                     |
| ☐                                                   |     | Fee paid previously with preliminary materials                                                      |
| ☐                                                   |     | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11 |

| AUTOMATIC DATA PROCESSING, INC. 
 1 ADP BOULEVARD                 
 ROSELAND, NJ 07068              |     | Your                                      
 Vote Counts!                              
 AUTOMATIC DATA PROCESSING, INC.           
 2025 Annual Meeting                       
 November 12, 2025, 10:00 a.m.             
 www.virtualshareholdermeeting.com/ADP2025 
 Vote by November 11, 2025 11:59 PM EST    |
|:--------------------------------|:----|:------------------------------------------|
| V78942-P36288                   |     |                                           |

You invested in AUTOMATIC DATA PROCESSING, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy materials for the stockholder meeting to be held on November 12, 2025. Get informed before you vote View the Combined Document containing Notice of 2025 Annual Meeting of Stockholders