TIN (Taxpayer Identification Number): What It Means for Employers

What it means in practice

What a TIN is. The IRS defines a taxpayer identification number as an identification number used in the administration of tax laws, issued either by the Social Security Administration (SSA) or by the IRS. The General Instructions for Certain Information Returns (2025) say TINs are used to match the amounts you report against the recipient's tax return. Publication 1281 adds that a TIN always has exactly nine digits and no letters; a number with more or fewer digits, or with a letter in it, is treated as missing. "TIN number" is a common way of saying the same thing, and this entry covers that phrase.

Social Security number (SSN). The SSN is the TIN for most individuals, issued by SSA on Form SS-5. Collecting, recording, verifying and correcting employee SSNs is covered in our Social Security number (SSN) entry and is not repeated here.

Employer identification number (EIN). The IRS TIN page says an EIN, also known as a federal tax identification number, identifies a business entity and is also used by estates and trusts. It is the number an employer puts on its own Forms 941 and W-2. How to apply for and use one is covered under employer identification number (EIN), and the IRS confirmation notice is covered under CP 575 letter.

Individual taxpayer identification number (ITIN). The IRS ITIN page describes a 9-digit number the IRS issues to people who need a U.S. TIN for federal tax purposes but are not eligible for an SSN. It begins with 9 and is applied for on Form W-7. The IRS says an ITIN is for federal tax purposes only and does not authorize work in the U.S. or change immigration status. A person cannot have both numbers; once an SSN is issued, the holder stops using the ITIN and notifies the IRS, which combines the records, or the person may not receive credit for all wages paid and taxes withheld. The Instructions for the Requester of Form W-9 (03/2024) say an ITIN not used on a federal tax return at least once in the last 3 consecutive tax years expires.

Adoption taxpayer identification number (ATIN). An ATIN is a temporary nine-digit number the IRS issues, on Form W-7A, to people adopting a U.S. citizen or resident child who cannot get the child's SSN in time to file their return. The IRS ATIN questions and answers say it generally takes 4 to 8 weeks to issue and is deactivated once the IRS learns the child's SSN or automatically after two years. ATINs are rarely seen in payroll, though the General Instructions list them among individual recipient TINs.

Preparer tax identification number (PTIN). The IRS says anyone who prepares or assists in preparing federal tax returns for compensation needs a valid PTIN; the fee for 2027 PTINs is $18.75. The Instructions for Form 941 (03/2026) tell a paid preparer to enter a PTIN in the paid preparer section and the firm's EIN, and say a PTIN cannot replace the firm's EIN. The IRS PTIN FAQ says an employee who prepares the employer's own returns as part of the job does not need a PTIN, and lists the Form W-2 series, the Form 1099 series and Form SS-4 among forms excluded from the PTIN requirement.

Which number goes where. Under 26 CFR 301.6109-1(a)(1)(ii), an individual uses an SSN, or an ITIN if not eligible for one; non-individuals such as corporations, partnerships, trusts and estates use an EIN; and an individual employer or sole proprietor uses an EIN where a return requires one. The regulation also says the ITIN "does not refer to a social security number or an account number for use in employment for wages," which is why it never goes in box a of Form W-2. Publication 15 (2026) says not to use an SSN or ITIN on forms that ask for an EIN.

Employees versus payees. For employees, the employer collects the SSN and reports it on Form W-2; the W-2 instructions say an ITIN holder who becomes eligible to work must get an SSN. For contractors and other payees reported on Form 1099, the payee may give an SSN, ITIN or EIN. The General Instructions say a sole proprietor is reported under the individual's name with either the SSN or the business EIN (the IRS prefers the SSN), a disregarded single-member LLC under the owner's name and number, and an LLC taxed as a corporation or partnership under its own EIN.

Certifying the TIN on Form W-9. The General Instructions suggest Form W-9 for U.S. payees and Form W-8 for foreign payees. On Form W-9 (Rev. March 2024) the payee certifies under penalties of perjury that the number is correct (or that a number is pending), that the payee is not subject to backup withholding, that the payee is a U.S. person, and that any FATCA code is correct. A resident alien not eligible for an SSN enters an ITIN in the SSN space, and the requester instructions say an expired ITIN may still be used on Form W-9. A payee without a number may write "Applied For," but the 60-day grace period applies only to interest, dividends and certain readily tradable instruments; nonemployee compensation is subject to backup withholding immediately. W-9 information must be kept confidential. See Form W-9 for the form itself.

Checking TINs before you file: TIN Matching. The IRS TIN Matching service, part of IRS e-Services, lets payers and their authorized agents validate name and TIN combinations before filing information returns. The IRS page says a payer must be listed in the IRS Payer Account File, to which payers are added if they filed Forms 1099 to report backup withholding within the last 2 years, and must apply through an IRS account. Publication 2108 (Rev. 11-2024) describes interactive checks of up to 25 combinations with results in real time and bulk files of up to 100,000 returned within 24 hours, at no fee. It also says the program cannot enroll employers for Form W-2 purposes; for employee SSNs, Publication 15 points employers to SSA's Social Security Number Verification Service (SSNVS). Under Publication 2108, not participating is not held against a payer's reasonable cause, a documented positive match can support a penalty waiver request, and results are confidential.

Backup withholding. The requester instructions list four triggers: the payee fails to furnish a TIN; the IRS notifies the payer that a TIN is incorrect; the IRS notifies the payer of payee underreporting of interest or dividends; or the payee fails to certify that it is not subject to backup withholding. The payer then withholds 24 percent of reportable payments until the cause is fixed, and may become liable for amounts it fails to withhold. Publication 15 (2026) says backup withholding does not apply to wages and is reported on Form 945, not Form 941. Under the General Instructions, a payer that backup withholds must file the Form 1099 and furnish a statement even when the payment is below the normal reporting threshold.

CP2100 notices and B notices. After you file, the IRS sends a CP2100 or CP2100A notice listing payees whose name and TIN did not match; Publication 1281 says filers with 50 or more error documents receive a CP2100 and smaller filers a CP2100A. If the mistake was yours, correct your records and send no B notice. If your records agree with the list, send a B notice within 15 business days of the notice date or the date you received it, whichever is later, in an envelope marked "IMPORTANT TAX INFORMATION ENCLOSED" or "IMPORTANT TAX RETURN DOCUMENT ENCLOSED." The first B notice goes with a Form W-9. Begin backup withholding no later than 30 business days after that date if no signed W-9 comes back, and stop within 30 calendar days of receiving one.

The second B notice. If the same account appears again within three calendar years, Publication 1281 calls for the second B notice, sent without a Form W-9. The payee must then validate the number with the issuing agency: an individual sends a copy of a Social Security card, an EIN holder sends IRS Letter 147C, an ITIN holder sends Letter 685C and an ATIN holder sends Letter 096C. If the validation has not arrived by the 30th business day after the second notice, backup withholding begins and continues until it does. Payers must track the notices themselves, because a CP2100 does not say whether it is a first or second notification.

Penalties and reasonable cause. Sections 6721 and 6722 penalize returns and payee statements without a correct TIN. Publication 1586 says that to show reasonable cause a filer must have acted in a responsible manner before and after the failure, which generally means an initial solicitation for the TIN when the relationship begins and, if needed, annual solicitations, and must show significant mitigating factors or events beyond its control. A Notice 972CG proposing a penalty must be answered within 45 calendar days of the notice date (60 for foreign filers). Sending the required B notices for the same payees satisfies the annual solicitation requirement.

Truncated TINs on payee statements. Under 26 CFR 301.6109-4, a truncated TIN replaces the first five digits with Xs or asterisks (XXX-XX-1234 for an SSN, XX-XXX1234 for an EIN). Truncation is optional and is not allowed on documents filed with the IRS or SSA, where the full number is specifically required, or on the filer's own TIN; the regulation's example is an employer that may truncate employee SSNs on employee W-2 copies but not its own EIN. The General Instructions add that the payee TIN may not be truncated on Form W-2G.

Example 1 (illustration): a contractor with no TIN. In 2026 a business engages a sole proprietor who does not provide a TIN and pays $3,000 for services. Because nonemployee compensation has no 60-day grace period, backup withholding applies at 24 percent: $3,000 x 0.24 = $720. The business pays $2,280, reports the $3,000 and the $720 withheld on Form 1099-NEC with the TIN box blank, and reports the $720 on Form 945.

Example 2 (illustration): counting B notice days. A CP2100A dated Monday, March 2, 2026 arrives Thursday, March 5. The later date, March 5, starts the count. Counting weekdays only (no federal holidays fall in this window), the 15th business day is Thursday, March 26, the deadline to mail the first B notice with Form W-9. The 30th business day is Thursday, April 16, 2026; if no signed W-9 has come back, backup withholding must begin on payments by then.

Recordkeeping. The General Instructions say to keep copies of information returns for at least 3 years from the due date, or 4 years if backup withholding was imposed. Publication 1281 says to track accounts for three years after the first CP2100 notice and keep an undeliverable B notice for three years.

Where states differ. The W-2 instructions tell employers to check with state, local or territorial governments on whether truncated SSNs are allowed on W-2 copies sent to them, and state wage reporting and state information return rules are set by each state agency.

Question: Can TIN Matching check new hires? No. It covers Form 1099 payees subject to backup withholding; employee SSNs are checked through SSA's SSNVS.

Question: Is backup withholding taken from employee wages? No. Publication 15 excludes wages; employees are subject to regular income tax withholding.

This entry explains the federal TIN rules and does not decide which number a particular worker or payee should give or how a specific notice should be answered.

Why it matters and common mistakes

How Remindax helps

Related terms

See all terms in Tax Forms & Government Filings or browse the full HR Glossary.