Your tax identification number sits on documents you already have. For most individuals that number is a Social Security Number, printed on prior Form 1040s, W-2s, 1099s, and the card itself. Businesses use an Employer Identification Number, which appears on the IRS confirmation letter (CP 575), payroll returns, and business bank paperwork. People who file with the IRS but aren’t eligible for an SSN use an Individual Taxpayer Identification Number, first issued on a CP565 notice and reused on every return afterward. If you know which type of number you need, the fastest place to find your tax ID number is almost always a document already in your files; if nothing turns up, the IRS and the Social Security Administration will look it up for you.
Finding Your Social Security Number
Federal law requires your SSN on every return, wage report, and financial statement you file.1Office of the Law Revision Counsel. 26 USC 6109 – Identifying Numbers Because it appears in so many places, you rarely need to request it from the government. Check these first:
- A prior year’s Form 1040. The SSN field is at the top of page one, next to your name.
- Your W-2, in the box labeled “Employee’s social security number.”
- Any 1099 you received, in the “Recipient’s TIN” box.
- Your physical Social Security card, the original source document issued by the SSA.
You can also pull a tax return transcript through your IRS online account, by calling the automated transcript line at 800-908-9946, or by mailing Form 4506-T.2Internal Revenue Service. Online Account and Tax Transcripts Can Help Taxpayers File a Complete and Accurate Tax Return Transcripts partially mask the SSN for security, but they can confirm you have the right number if you’re second-guessing a digit.
If none of that works, you need a replacement card from the Social Security Administration, not the IRS. Request one online through the my Social Security portal at ssa.gov, or schedule an appointment at a local SSA field office if the online option isn’t available for your situation.3Social Security Administration. Replace Social Security Card An in-person visit requires a government-issued photo ID such as a driver’s license or passport. You’re capped at three replacement cards per year and ten in your lifetime, though cards issued for a legal name change or a change to the work-authorization legend don’t count against the limit.4Federal Register. Social Security Number (SSN) Cards; Limiting Replacement Cards
Finding Your ITIN
If you’re not eligible for an SSN but file a federal return, the IRS assigns you a nine-digit ITIN. It goes in the same spot on Form 1040 where an SSN would.5Internal Revenue Service. Individual Taxpayer Identification Number (ITIN) The single best source is the CP565 notice the IRS mailed you when the number was first assigned. If you no longer have it, look at any tax return you’ve filed since then; the ITIN appears in the same field an SSN would.6USAGov. Get an Individual Taxpayer Identification Number (ITIN) to File Your Tax Return
Don’t apply for a new ITIN just because you lost the old one. The IRS expects you to keep using the number you were assigned. To have the agency look it up, call 800-829-1040, or 267-941-1000 from outside the United States.5Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
Finding Your EIN
Businesses, partnerships, trusts, and certain other entities use an EIN as their federal tax ID. The IRS assigns the nine-digit number when you submit Form SS-4.7Internal Revenue Service. About Form SS-4, Application for Employer Identification Number (EIN) If you applied online, the IRS issued the EIN immediately and let you print a confirmation. About four to six weeks later, it mails an official CP 575 letter. That letter is the primary proof of your EIN, and banks and lenders often ask for it. The IRS will not reissue a duplicate CP 575 if you lose it.8Internal Revenue Service. Employer Identification Number
If the CP 575 is gone, the EIN is on plenty of other records:
- Form 941, the quarterly payroll tax return, carries it in the header on every page.9Internal Revenue Service. Form 941 – Employer’s Quarterly Federal Tax Return
- Business bank statements and the paperwork you signed when the account was opened.
- Prior business tax returns — Forms 1120, 1120-S, 1065, and other entity returns all show the EIN near the top.
- State license and permit filings that required the EIN when you submitted them.
When those turn up nothing, call the IRS Business and Specialty Tax Line at 800-829-4933, Monday through Friday, 7 a.m. to 7 p.m. local time.10Internal Revenue Service. Telephone Assistance Contacts for Business Customers The agent will verify your identity before releasing the number, so have your name, your personal tax ID, and details about the business ready. You can also ask for a 147C verification letter, which serves as official proof of your EIN in place of the CP 575 and typically arrives within 10 to 14 business days.8Internal Revenue Service. Employer Identification Number
Two Less Common Tax IDs
Two other IRS-issued numbers come up in narrower situations.
Preparer Tax Identification Number
Anyone who prepares federal tax returns for compensation needs a valid PTIN, and enrolled agents must maintain one as well.11Internal Revenue Service. PTIN Requirements for Tax Return Preparers If you’ve forgotten yours, sign in to your IRS online PTIN account; the number is displayed there.
Adoption Taxpayer Identification Number
An ATIN is a temporary tax ID the IRS issues for a child in a domestic adoption when the adopting parents can’t yet get the child’s SSN. It lets you claim the child as a dependent or take the child care credit while the adoption is pending. The application is Form W-7A, filed with the IRS Austin Service Center along with your placement documentation, and you should apply at least eight weeks before your tax return is due.12Internal Revenue Service. Adoption Taxpayer Identification Number
What Happens if You Don’t Provide One
Leaving your tax ID off financial paperwork has a direct cost. When a payee fails to give a correct TIN, or provides one that’s clearly wrong, the payer is required to withhold 24% of the payment and send it to the IRS as backup withholding.13Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide A freelancer who never gave a client an SSN will see nearly a quarter of each payment routed to the IRS before it reaches them. The money is reconciled when you file your return, but the cash-flow hit in the meantime is real.14Office of the Law Revision Counsel. 26 US Code 3406 – Backup Withholding Worth tracking down the number before the next payment goes out.