A filer’s federal ID number is the taxpayer identification number (TIN) that the IRS uses to link a return to a specific person or business. For most individuals, that’s a Social Security Number (SSN). For most businesses, it’s an Employer Identification Number (EIN). People with a U.S. tax obligation who can’t get an SSN use an Individual Taxpayer Identification Number (ITIN) instead. The number appears on every tax return and information return you file, and leaving it off or getting it wrong triggers withholding and penalties.1Internal Revenue Service. Taxpayer Identification Numbers
Which Number Applies to You
The IRS recognizes five kinds of TIN, but three cover almost every filer.1Internal Revenue Service. Taxpayer Identification Numbers
If you’re a U.S. citizen or an authorized resident filing your own return, your SSN is your federal ID. It goes on Form 1040, and you give it to employers, banks, and brokerages so they can report your income accurately on W-2s and 1099s.
If you run a corporation, partnership, or multi-member LLC, or if your business hires employees, you file under an EIN. Estates and certain trusts also need their own EIN.2Internal Revenue Service. Employer Identification Number
If you have a U.S. filing obligation but aren’t eligible for an SSN, the IRS issues an ITIN. It’s a nine-digit number starting with 9, formatted 9XX-XX-XXXX, and it goes wherever an SSN would go on Form 1040 and its schedules.3Internal Revenue Service. Individual Taxpayer Identification Number
Two other TINs exist for narrow cases and aren’t something a typical filer needs. An Adoption Taxpayer Identification Number (ATIN) is temporary, assigned to a child in a pending adoption when the adoptive parents can’t yet get the child’s SSN. A Preparer Taxpayer Identification Number (PTIN) is required for anyone who prepares federal returns for pay; the application and annual renewal fee is $18.75.4Internal Revenue Service. PTIN Requirements for Tax Return Preparers
The Sole Proprietor Question
A sole proprietor with no employees can legally use a personal SSN as the business’s federal ID on Schedule C. Nothing requires an EIN in that situation. The catch is practical: every client who pays you asks for a W-9, and using your SSN means putting it on every one of those forms. Many sole proprietors apply for an EIN specifically to keep the SSN off invoices and contractor paperwork. The EIN is free and issued online in minutes, so the privacy benefit costs nothing.5Internal Revenue Service. Get an Employer Identification Number
ITINs Expire — and That Matters
An ITIN doesn’t stay valid forever. If you don’t use yours on a federal return for three consecutive tax years, it goes inactive automatically. Filing with an expired ITIN delays processing, holds up refunds, and forces you to renew before the IRS will finish anything. To renew, you submit a new Form W-7 with your return and the required identity documents.3Internal Revenue Service. Individual Taxpayer Identification Number
When a Business Needs a New EIN
An EIN doesn’t follow a business through every change. Some structural events require applying for a fresh number:6Internal Revenue Service. Do You Need a New Employer Identification Number (Publication 5845)
- A sole proprietorship that incorporates or takes on partners to form a partnership.
- A corporation that receives a new charter from the secretary of state, becomes a subsidiary, converts to a partnership or sole proprietorship, or forms a new corporation through statutory merger.
- A partnership that incorporates, dissolves to become a sole proprietorship, or ends and re-forms as a new partnership.
A simple name change usually does not require a new EIN. You report it on the next return by checking the appropriate box on Form 1120, 1120-S, or 1065. Sole proprietors send written notice to the IRS at the address where they file.7Internal Revenue Service. Business Name Change
How to Get One
EIN
The fastest route is the IRS online application, which issues the EIN immediately. Faxing Form SS-4 takes about four business days; mailing it takes roughly four weeks.8Internal Revenue Service. Instructions for Form SS-4 You’ll need the entity type, the business address, and the SSN or ITIN of the responsible party. The responsible party must be a real person who controls or directs the organization, not another entity.9Internal Revenue Service. Responsible Parties and Nominees
ITIN
You apply with Form W-7 along with original or certified copies of identity and foreign status documents. The application can be mailed, filed in person at an IRS Taxpayer Assistance Center, or submitted through an IRS-authorized Certifying Acceptance Agent. Going in person or using an acceptance agent lets you avoid mailing original documents like a passport.10Internal Revenue Service. About Form W-7, Application for IRS Individual Taxpayer Identification Number
SSN
U.S. citizens and eligible noncitizens apply through the Social Security Administration on Form SS-5. You provide documents proving citizenship or immigration status, age, and identity. A current U.S. passport can prove citizenship and identity in a single document.11Social Security Administration. Request Social Security Number for the First Time Noncitizens generally need work authorization from the Department of Homeland Security to qualify.12Social Security Administration. Social Security Numbers for Noncitizens
Where the Number Goes on Tax Forms
Your federal ID sits near the top of every primary tax document. On Form 1040, your SSN or ITIN identifies whose liability is being calculated. On Form W-2, the employer’s EIN appears in box b and the employee’s SSN in box a.13Internal Revenue Service. Form W-2 – Wage and Tax Statement
On information returns like 1099-NEC, two TINs appear: the payer’s and the recipient’s. A business paying an independent contractor reports its own EIN as the payer’s TIN and the contractor’s SSN or ITIN as the recipient’s TIN. The IRS uses this pairing to match the reported payment against the recipient’s personal return.
Form W-9
Before a business can file a 1099, it needs the payee’s TIN. That’s the job of Form W-9. If you’re a freelancer or independent contractor, expect to fill one out before work starts. It collects 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 If the Number Is Missing or Wrong
Two consequences hit, one on each side of the transaction.
Backup Withholding on the Payee
If you fail to give a payer your TIN, provide the wrong one, or the IRS tells the payer your TIN doesn’t match, the payer must withhold 24% of your payment and send it to the IRS. You can claim the withheld amount back when you file, but that money is locked up until then. Backup withholding applies to most reportable payments that would otherwise appear on a 1099, including interest, dividends, and nonemployee compensation.15Internal Revenue Service. Tax Withholding Types16Office of the Law Revision Counsel. 26 USC 3406 – Backup Withholding
Penalties on the Payer
Businesses that file information returns with a missing or wrong TIN owe a per-return penalty that grows the longer the error stands. For returns due in 2026:17Internal Revenue Service. Information Return Penalties
- Corrected within 30 days: $60 per return.
- Corrected after 30 days but by August 1: $130 per return.
- Corrected after August 1 or never filed: $340 per return.
- Intentional disregard: $680 per return.
The annual cap is $3,000,000 for most filers, and $1,000,000 for businesses with average gross receipts of $5,000,000 or less over the prior three years.18Office of the Law Revision Counsel. 26 USC 6721 – Failure to File Correct Information Returns For a business issuing hundreds of 1099s, the exposure grows quickly. Collecting a correct W-9 before making any payment is the cleanest way to avoid the whole problem.