What is Taxpayer Identification Number (TIN)?

Every tax return and most information returns require a taxpayer identification number, or TIN. The IRS describes the types on its taxpayer identification numbers page.

Types of TIN

• Social Security number (SSN): issued by the Social Security Administration to individuals
• Employer identification number (EIN): issued by the IRS to businesses, trusts, estates and other entities; required for employers, corporations and partnerships. See how to get an EIN
• Individual taxpayer identification number (ITIN): issued by the IRS to individuals who need a TIN but are not eligible for an SSN
• Adoption taxpayer identification number (ATIN): a temporary number for certain adoption cases
• Preparer tax identification number (PTIN): used by paid tax return preparers

Using the right TIN

Businesses use their EIN for payroll, business returns and on Form W-9 when requested. A sole proprietor without an EIN may use their SSN, though getting an EIN keeps the SSN private. For a single-member disregarded entity, the owner's TIN is often used for income tax purposes, while the LLC's own EIN is used for payroll.

Mismatches

When a name and TIN on an information return do not match IRS records, the payer may receive a notice and need to begin backup withholding. Collecting accurate information at onboarding prevents this.

Protecting TINs

SSNs and EINs are sensitive. Store W-9s and employee records securely and limit who can see them.

Related terms

• Disregarded Entity: A disregarded entity is a business entity, usually a single-member LLC, that is ignored as separate from its owner for federal income tax purposes.
• Backup Withholding: Backup withholding is federal income tax a payer must withhold from certain payments when the payee's taxpayer identification number is missing or incorrect.

Browse more definitions in the small business glossary.