National Insurance number
United Kingdom · Individuals
Paste or type the number — punctuation is optional.
Other identifiers
Europe
Asia and the Middle East
Oceania
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.
How the NINO check works, and what the number tells you
A NINO is a personal identity number issued in United Kingdom. This page checks one against the published rule, shows which specific test it fails when it fails, and decodes the facts the digits carry. Everything runs in your browser — the number you type is never sent anywhere.
How it works
- Applies the published checksum rather than only checking the length and shape.
- Names the exact rule that failed, so a typo is distinguishable from a number that was never valid.
- Decodes what the number encodes: prefix.
- Does not generate numbers. This one identifies a person, and a page that manufactures plausible identity numbers is a liability rather than a feature.
9 characters: AA NNNNNN S first letter not D, F, I, Q, U or V second letter not D, F, I, O, Q, U or V prefix never BG, GB, KN, NK, NT, TN or ZZ suffix A, B, C or D There is no check digit. A National Insurance number can only be checked against format and the exclusion lists above.
Worked example
Checking AB123456C, a valid NINO, digit by digit.
- input AB123456C
- normalised AB 12 34 56 C
- Prefix AB
- Checksum None — a NINO has no check digit
- result passes every published check
The checksum passes, so the number is internally consistent, and the tool reads off prefix. Internal consistency is not the same as the number being issued to somebody — see the note below.
Reading the result
- QQ123456C is the placeholder HMRC uses in its own documentation, and it is deliberately invalid — Q is never issued as a first letter. That is a useful property: a number that looks like an example probably is one.
- A passing checksum means the digits are consistent with each other, not that the number exists. Only United Kingdom's own registry can tell you whether a number was actually issued and is still valid, and no offline tool can substitute for that.
- The check happens entirely in your browser. Nothing is uploaded, logged, or stored, which matters more here than on most tools because these numbers are personal data in every jurisdiction that issues them.
- Punctuation is ignored. Spaces, dots, dashes and slashes are stripped before the check, so a number pasted in any common local format is read the same way.
Common questions
- My number is real but this says it is not valid. Why?
- Check for a transposed pair of digits first — that is the single most common cause, and every checksum here is designed to catch it. Failing that, the number may predate the current rule: several countries changed or introduced their checksum at a known date, and older numbers were not reissued. If the tool names a specific rule that failed, that is the one to look at.
- Does a valid result mean the number is registered?
- No, and this is the limit worth understanding. A checksum proves the digits are mutually consistent, which catches typos and made-up numbers. It cannot prove the number was issued, is still active, or belongs to the person quoting it. Only the issuing authority's own lookup can do that.