US SSN Format Validator

US Social Security Number (SSN): format, invalid ranges and why there's no checksum

The Social Security Number (SSN) is the United States' de-facto national identifier, issued by the Social Security Administration (SSA). The format is 9 digits grouped as AAA-GG-SSSS — three parts historically called the Area (3 digits), Group (2 digits) and Serial (4 digits). There is no check digit: an SSN cannot be verified by arithmetic alone, only by its structural rules and (officially) by the SSA's records.

Because there's no checksum, validation relies on excluded ranges the SSA never issues:

• Area cannot be 000, 666, or any value in 900–999 (the 900 range is reserved for ITINs).
• Group cannot be 00.
• Serial cannot be 0000.
• Well-known invalid/advertising numbers (e.g. 078-05-1120, the Woolworth wallet card; 123-45-6789) should be rejected by careful validators.

Randomization since 2011

Until June 2011 the Area code encoded the state where the number was issued and the Group followed a documented issuance order. Since SSN randomization in 2011, the Area no longer maps to geography and previously unused Area numbers (like the 700s) became available — so any geography-based "validation" is now obsolete. Structural range checks remain valid.

Common pitfalls

• Treating it as verifiable: a structurally valid SSN is not proof of identity — only the SSA's Consent Based SSN Verification (CBSV) confirms a real assignment.
• Confusing SSN with ITIN: ITINs also have 9 digits but always start with 9 — see the ITIN validator.
• Storing real SSNs: SSNs are highly sensitive PII; use this tool for format checks and synthetic test data, never to harvest live numbers.

FAQ

Does an SSN have a check digit? No. It is validated by structure (excluded ranges) plus the SSA's authoritative records.

Can the Area tell me the issuing state? Only for numbers issued before mid-2011. After randomization the Area carries no geographic meaning.

Is 123-45-6789 valid? Structurally it passes the range rules, but it's a famous placeholder and most validators (and the SSA) treat it as invalid.