A filer’s federal identification number is the taxpayer identification number (TIN) the IRS uses to tie a return, a W-2, or a 1099 to the right person or business. For an individual, that’s almost always a Social Security Number (SSN). For a business, it’s an Employer Identification Number (EIN). People who owe U.S. tax but can’t get an SSN use an Individual Taxpayer Identification Number (ITIN) instead.1Internal Revenue Service. Taxpayer Identification Numbers Getting the number right matters: a missing or wrong TIN triggers 24% backup withholding on the payee and per-return penalties on the payer.
Which Number Applies to You
If you’re a U.S. citizen or a noncitizen authorized to work in the United States, your SSN is your federal ID for tax purposes. It goes on your Form 1040, and you hand it to employers, banks, and brokerages so the income they report lines up with your return.1Internal Revenue Service. Taxpayer Identification Numbers
If you have a U.S. tax filing obligation but aren’t eligible for an SSN, the IRS issues an ITIN. It’s a nine-digit number that always starts with 9, formatted 9XX-XX-XXXX, and you use it anywhere an SSN would otherwise go on a 1040.2Internal Revenue Service. Individual Taxpayer Identification Number One trap worth knowing: an ITIN that doesn’t appear on a federal return for three consecutive tax years automatically becomes invalid. Filing with an expired ITIN delays processing and holds up any refund until you renew by submitting a new Form W-7 with your return.
Businesses use an EIN. That covers corporations, partnerships, multi-member LLCs, nonprofits, estates, certain trusts, and any sole proprietorship or single-member LLC with employees.3Internal Revenue Service. Employer Identification Number The EIN appears on Form 1120 for corporations, Form 1065 for partnerships, employment tax returns, and every W-2 or 1099 the business issues.
Two other TINs exist and are worth naming only so you can rule them out: the Adoption Taxpayer Identification Number (ATIN), a temporary number for a child in a pending adoption, and the Preparer Taxpayer Identification Number (PTIN), required for anyone paid to prepare federal returns.4Internal Revenue Service. PTIN Requirements for Tax Return Preparers Neither is something an ordinary filer needs.
Sole Proprietors: SSN or EIN?
Run a business by yourself with no employees and you’re allowed to use your personal SSN as the business’s federal ID on Schedule C. That’s legal, but it means putting your SSN on every W-9 a client asks for. Many sole proprietors apply for an EIN just to keep their SSN off invoices and contractor paperwork. The EIN is free and the online application takes minutes, so the privacy upside costs nothing.5Internal Revenue Service. Get an Employer Identification Number
How to Get Each Number
EIN
The fastest route is the IRS online application, which issues the number immediately. Faxing Form SS-4 takes about four business days; mailing it takes around four weeks.6Internal Revenue Service. Instructions for Form SS-4 Before you start, know your entity type and have the business address and the responsible party’s SSN or ITIN on hand. The responsible party has to be a real person who controls or directs the organization, not another entity.7Internal Revenue Service. Responsible Parties and Nominees
Your EIN doesn’t carry across every structural change. A sole proprietor who incorporates or takes on partners needs a new one. A corporation that gets a new charter, becomes a subsidiary, converts to a partnership or sole proprietorship, or forms a new entity through statutory merger needs a new one. A partnership that incorporates, dissolves into a sole proprietorship, or ends and reforms needs a new one.8Internal Revenue Service. Do You Need a New Employer Identification Number (Publication 5845) A plain name change usually doesn’t.9Internal Revenue Service. Business Name Change
ITIN
Submit Form W-7 with original or certified copies of identity and foreign status documents. You can mail the application, go in person to an IRS Taxpayer Assistance Center, or work through an IRS-authorized Certifying Acceptance Agent. The in-person and acceptance-agent routes let you avoid putting original documents like a passport in the mail.10Internal Revenue Service. About Form W-7, Application for IRS Individual Taxpayer Identification Number
SSN
Apply through the Social Security Administration using Form SS-5. You’ll show documents proving citizenship or immigration status, age, and identity. A current U.S. passport covers both citizenship and identity in one document.11Social Security Administration. Request Social Security Number for the First Time Noncitizens generally need Department of Homeland Security work authorization to qualify.12Social Security Administration. Social Security Numbers for Noncitizens
Where the Number Shows Up
Your TIN sits near the top of every primary tax document. On Form 1040 it identifies whose liability is being calculated. On a W-2, the employer’s EIN goes in box b and the employee’s SSN in box a.13Internal Revenue Service. Form W-2 – Wage and Tax Statement
On a 1099-NEC, there’s a payer TIN and a recipient TIN. If a business pays an independent contractor, the business’s EIN is the payer TIN and the contractor’s SSN or ITIN is the recipient TIN. The IRS uses that pairing to match the payment against the recipient’s personal return, which is why a mismatch anywhere in the chain creates problems.
Form W-9
Before a business can issue a 1099, it needs the payee’s TIN. Form W-9 collects it. If you’re a contractor or freelancer, expect to complete one before any work begins; the form asks for your name, address, TIN, and a certification that the number is correct.14Internal Revenue Service. About Form W-9, Request for Taxpayer Identification Number and Certification
What Happens When the TIN Is Missing or Wrong
Two different consequences, one on each side of the transaction.
Backup Withholding Hits the Payee
If you don’t give a payer your TIN, give an incorrect one, or the IRS tells the payer your number doesn’t match, the payer must withhold 24% of your payment and send it to the IRS. It’s not an extra tax: you claim the withheld amount when you file. But a quarter of your income is tied up until then.15Internal Revenue Service. Tax Withholding Types It applies to most reportable payments that would otherwise land on a 1099, including interest, dividends, and nonemployee compensation.16Office of the Law Revision Counsel. 26 USC 3406 – Backup Withholding
Penalties Hit the Payer
Businesses that file information returns with a missing or wrong TIN pay per-return penalties that climb with delay. For returns due in 2026:17Internal Revenue Service. Information Return Penalties
- $60 per return if corrected within 30 days
- $130 per return if corrected after 30 days but by August 1
- $340 per return if corrected after August 1 or never filed
- $680 per return for intentional disregard
The annual cap is $3,000,000 for most filers, with a lower $1,000,000 cap for businesses whose average gross receipts over the prior three years are $5,000,000 or less.18Office of the Law Revision Counsel. 26 USC 6721 – Failure to File Correct Information Returns For a business issuing hundreds of 1099s, those per-return numbers add up quickly. Collecting a correct, signed W-9 before any payment goes out is the cheapest preventive step there is.