How Does an S Corporation Fill Out a W-9?
Which box to check on Line 3, whose name and TIN to use — for 2026.
By the Easy Guides Editorial Team · Updated for 2026
On a W-9 for an S Corporation, the key is Line 3a: check the S Corporation box. Put the corporation's legal name on Line 1, and use the corporation's EIN (never a personal SSN) as the taxpayer ID. Get those right and the rest of the form is straightforward.
Which box to check
On Line 3a, check the “S Corporation” box. (If your business is an LLC that elected S-corp taxation, instead check the “Limited liability company” box and enter S as the tax classification.)
Whose name goes on Line 1
Line 1 must show the corporation's legal name on Line 1. Line 1 is never left blank and never holds a trade name by itself — the IRS matches it against the taxpayer ID, so a mismatch triggers backup withholding.
Which taxpayer ID to use
Use the corporation's EIN (never a personal SSN). If you need one, an EIN is free from the IRS. See SSN vs EIN on a W-9 for which to use.
Everything else is the same
The remaining lines — address, and signing in Part II — work the same for every entity. Our line-by-line W-9 walkthrough covers them.