Form W-9, Request for Taxpayer Identification Number and Certification, is the IRS form a business uses to collect the correct taxpayer identification number (TIN) of a US person, including a resident alien, that it pays. The payee fills in its legal name, business name, federal tax classification, any exemption codes, address and TIN (a Social Security number or an employer identification number), and certifies the information under penalties of perjury.
The business that asks for it is the requester. It needs the TIN to file information returns with the IRS, for example Form 1099-NEC for nonemployee compensation. The requester keeps the W-9 in its records. It is not sent to the IRS.
Why it matters
Without a valid TIN, the payer may be required to start backup withholding on reportable payments, and information returns filed with a wrong name and TIN combination create problems later. Foreign persons do not use the W-9; they give the appropriate Form W-8 instead.
Example
Before paying a freelance designer for the first time (illustrative), accounts payable asks for a W-9 as part of supplier onboarding. At year end, it uses the name and TIN on file to prepare the 1099-NEC.
Common pitfalls
- Collecting W-9s at year end, when contractors are hard to reach.
- Sending them by plain email. The form can carry a Social Security number.
- Not checking the name and TIN. Payers that file information returns can validate them with the IRS TIN Matching service.
- Stale forms after a supplier changes its name or entity type.
This is a general summary, not tax advice. Check the IRS sources below.