Social Security Number
United States · Individuals
Paste or type the number — punctuation is optional.
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What this check does — and what it cannot do
This tool checks the number's structure and its check digit, using the published algorithm for that document. A number that passes is well formed: it is arithmetically consistent and could have been issued.
It cannot tell you whether the number was actually issued, whether it is active, or who it belongs to. Only the issuing tax authority can confirm that, through its own lookup service. Treat a passing result as "worth submitting", never as proof of identity.
The US Social Security number has no check digit at all
Most national identifiers end in a digit computed from the others, so a single typo fails arithmetically. The SSN does not. It has nine digits and no checksum, which means validation can only rule out numbers that were never issuable — and can never confirm that a number is real.
How it works
- Checks the three structural rules: the area, group and serial blocks each have values that are never assigned.
- Flags the well-known invalid patterns, including the 078-05-1120 that appeared on sample cards and was widely copied.
- Makes explicit what cannot be determined offline, which for the SSN is almost everything.
AAA-GG-SSSS area AAA never 000, never 666, never 900–999 group GG never 00 serial SSSS never 0000 there is no check digit — every other combination is structurally valid
Worked example
Testing a handful of numbers against the rules.
- 000-12-3456 — area 000, rejected
- 666-12-3456 — area 666, rejected
- 900-12-3456 — area in the 900s, rejected
- 123-00-4567 — group 00, rejected
- 123-45-6789 — structurally valid
123-45-6789 passes every rule there is. That tells you it could have been issued — nothing more. A mistyped digit in a genuine SSN almost always produces another structurally valid SSN, and no offline check will notice.
Reading the result
- This is the practical difference from an identifier like the Brazilian CPF: that one catches typos, the SSN cannot. If you are keying SSNs by hand, the error will reach your database intact.
- Since the 2011 move to randomised assignment, an SSN encodes nothing about where or when it was issued. Older validators that infer a state from the area number describe a scheme that no longer applies.
- 078-05-1120 was printed on specimen cards in a 1938 wallet promotion and was subsequently used by thousands of people who assumed it was theirs. It is permanently invalid, and it is why validators keep a blocklist.
- Treat an SSN as among the most sensitive fields you can hold. Verification against the Social Security Administration is the only authoritative check, and most systems that think they need to store an SSN do not.
Common questions
- Can a validator tell me if an SSN is real?
- No, and nothing offline can. It can only tell you the number is not structurally impossible. Confirming issuance requires the SSA's own verification service, which is restricted to employers and authorised parties.
- Why does my typo still pass?
- Because there is no check digit to violate. Changing one digit of a valid SSN nearly always yields another structurally valid SSN. Where correctness matters, the only defence is double entry or verification at the source.