What Is a Tax Identification Number (TIN)? Types and Uses

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A tax identification number (TIN), also called a taxpayer identification number, is a unique nine-digit number that the Internal Revenue Service (IRS) uses to identify a person or entity in the U.S. tax system. TIN is an umbrella term, not a single number. Your Social Security number (SSN) is a TIN, and so are the employer identification numbers (EINs) that businesses use and the individual taxpayer identification numbers (ITINs) issued to people who cannot get an SSN. The Social Security Administration issues SSNs; the IRS issues every other type.

Types of Tax Identification Numbers

The IRS recognizes five main types of TIN. Each applies to a specific kind of taxpayer or role.

• Social Security number (SSN): Issued by the Social Security Administration to U.S. citizens, permanent residents and certain temporary residents authorized to work. Formatted XXX-XX-XXXX. It is needed for legal employment and for Social Security benefits and other government services.
• Individual Taxpayer Identification Number (ITIN): Issued by the IRS to certain resident and nonresident aliens, their spouses and their dependents when they are ineligible for an SSN. It uses the same XXX-XX-XXXX layout but always starts with 9. Applicants file Form W-7 with documents that establish identity and foreign status.
• Employer Identification Number (EIN): Assigned to corporations, partnerships, trusts, estates, nonprofits and sole proprietors who need one (for example, because they have employees). It is also nine digits but written XX-XXXXXXX.
• Adoption Taxpayer Identification Number (ATIN): A temporary number for a child in a pending domestic adoption when the adoptive parents cannot yet get the child’s SSN. The child must be a U.S. citizen or permanent resident.
• Preparer Tax Identification Number (PTIN): Required for anyone who prepares all or part of a federal tax return for pay. The preparer enters it on each return they complete.

How a Tax Identification Number Works

A TIN links every tax record to one taxpayer. When an employer files a W-2, a bank files a 1099 for interest, or a broker reports the proceeds that later feed into capital gains tax, the form carries the recipient’s TIN. The IRS matches those information returns against the TIN on the taxpayer’s own return to confirm that reported income lines up.

Contractors and people opening investment accounts give payers their TIN on a W-9 form. If you do not provide a correct TIN, the payer may be required to apply backup withholding, holding back part of each payment and sending it to the IRS.

Interpreting a Tax Identification Number

The format tells you what kind of TIN you are looking at:

A PTIN begins with the letter P followed by eight digits, which keeps it visually separate from the nine-digit numbers above. The digits themselves do not encode income, tax status or creditworthiness; they only identify the holder.

Why a TIN Matters Beyond Taxes

The IRS requires a TIN on annual returns, but the number reaches further:

• Employment: Employers ask new hires for an SSN and verify it to confirm the person is authorized to work in the U.S.
• Credit: Banks and lenders request an SSN on credit applications. Credit bureaus use it to match applications and payment history to the right person.
• Business filings: Companies typically need a separate state tax ID from their state tax agency in addition to a federal EIN.

Example of a Tax Identification Number

Hypothetical example: Maria is a U.S. citizen who works full time and also earns money as a freelance designer.

• On her W-4 and tax return, she uses her SSN.
• She forms a single-member LLC and hires a part-time assistant. Because she now has an employee, she applies for an EIN (free from the IRS) and uses it for payroll filings.
• When a client sends her a W-9, she can give the EIN instead of her SSN, which limits how widely her SSN circulates.

Her cousin, living abroad, owns a U.S. rental property that produces income. He is not eligible for an SSN, so he applies for an ITIN with Form W-7 to file a U.S. return reporting that rental income.

Tax Identification Numbers Around the World

Most countries assign tax identifiers, though names and formats differ. Canada uses the Social Insurance Number (SIN), a nine-digit number written XXX-XXX-XXX, for employment, taxes, benefits and credit; the Canada Revenue Agency uses it for income tax. European Union member states issue national TINs that help tax authorities identify taxpayers in cross-border activity. Many businesses also hold a separate value-added tax registration number.

Limitations of a Tax Identification Number

A TIN identifies a taxpayer. It does not prove anything else about them.

• An ITIN is not work authorization. It does not make the holder eligible for Social Security benefits or change immigration status.
• ITINs can expire. An ITIN not used on a federal return for three consecutive years expires and must be renewed before use.
• An ATIN is temporary. Once the adoption is final and the child receives an SSN, the parents switch to the SSN.
• An EIN does not replace the owner’s SSN on the owner’s individual return.
• There is no public lookup for individuals. TINs are sensitive, so the issuing agency provides them on an official document (a Social Security card, an ITIN assignment letter or an EIN confirmation notice) rather than through an online directory.

Because one number ties together income, credit and employment records, a stolen SSN can be used for fraudulent returns or credit applications. Share it only when a legitimate payer, employer or lender requires it.

FAQs

The Bottom Line

Anyone who earns income, hires workers, prepares returns for pay or opens an investment account in the U.S. needs the right TIN for that role. Choose the number that fits your situation, such as an EIN for a business with employees or an ITIN if you cannot get an SSN. Share your SSN only with a legitimate payer, employer or lender, since one stolen number can expose tax, credit and employment records.