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UK National Insurance Number Validator

Finance & Global IDs

Validate a UK National Insurance Number (NIN) format instantly. Checks letter restrictions, reserved prefixes, and suffix rules — entirely in your browser.

What is a UK NIN?

A UK National Insurance Number Validator checks whether a NIN follows the exact structural rules HMRC uses when issuing these numbers — the right combination of letters and digits, with several specific exclusions that catch many common typos and invalid numbers immediately. A NIN follows the format two letters, six digits, one letter (for example, AB123456C), but several letter combinations are specifically disallowed by the official numbering scheme.

This validator checks every one of those rules — banned first and second letters, reserved two-letter prefixes, and valid suffix letters — and tells you immediately whether a number is correctly formed. For the equivalent US identifier, see the SSN Validator, and for the Canadian equivalent, see the Canada SIN Validator.

How to use this UK NIN calculator

  1. Enter the National Insurance Number in the National Insurance Number field, with or without spaces.
  2. Read the result card to see whether the number passed validation.
  3. If it failed, check the details or message to see exactly which rule was violated.
  4. Compare the number against the original document — payslip, P60, or HMRC letter — to find the discrepancy.
  5. Correct the number and re-check until it passes.

Formula & Methodology

A NIN is validated against four structural rules, checked in sequence:

1. Format: must match exactly 2 letters, 6 digits, 1 letter (spaces stripped first).
2. First letter: must not be D, F, I, Q, U, or V.
3. Second letter: must not be D, F, I, Q, U, V, or O.
4. Prefix: the first two letters together must not be BG, GB, NK, KN, TN, NT, or ZZ.
5. Suffix: the final letter must be A, B, C, or D.

Worked example: AB 12 34 56 C → normalised to AB123456C
- First letter "A" ✓, second letter "B" ✓, prefix "AB" not reserved ✓, suffix "C" ✓ → valid.

Invalid example: GB123456C fails immediately, since "GB" is a reserved prefix.

Frequently Asked Questions

A National Insurance Number (NIN or NINO) is a unique personal reference number used by HMRC and the Department for Work and Pensions to track an individual's National Insurance contributions, tax records, and eligibility for state benefits. It follows a fixed format of two letters, six digits, and one letter — for example, AB123456C.
The validator checks the overall format (2 letters, 6 digits, 1 letter), then applies the specific letter rules HMRC uses: certain letters are never used as the first or second letter, certain two-letter prefixes are permanently reserved and never issued, and the final letter must be A, B, C, or D.
HMRC excludes D, F, I, Q, U, and V from the first letter position, and additionally excludes O from the second letter position, to avoid confusion with similar-looking characters and to keep the numbering scheme consistent. These exclusions are part of the official format, not an arbitrary restriction.
BG, GB, NK, KN, TN, NT, and ZZ are permanently reserved and have never been allocated to a real NIN — GB and NK in particular are excluded because they could be confused with the country code or other administrative codes. A NIN starting with any of these prefixes is automatically invalid.
No — a passing result only confirms the number follows the correct structural rules, not that it has actually been issued by HMRC or belongs to a real person. Verifying an actual NIN requires official confirmation through HMRC or the Department for Work and Pensions.
The suffix letter was historically used to indicate how often National Insurance contributions were collected, though it no longer carries that operational meaning today. It must still be one of A, B, C, or D for the number to be considered correctly formatted.
Yes — NINs are often printed with spaces in pairs (AB 12 34 56 C), and this validator accepts that format as well as a continuous string, stripping spaces automatically before checking.
No — validation happens entirely in your browser using JavaScript. Your NIN is never sent to a server, logged, or stored, which matters given how sensitive this number is.
Both are personal tax and benefits identifiers, but they use completely different formats and validation rules — a NIN is 2 letters + 6 digits + 1 letter, while a US Social Security Number is purely 9 digits with its own area/group/serial range rules. Use the [SSN Validator](/ssn-validator/) for US numbers instead.
Your NIN appears on your payslip, P60, tax return, or any official HMRC correspondence. If you can't find it, you can request confirmation directly from HMRC through their official online services.
Also known as
NIN checkerNational Insurance number formatUK NI number validatorverify National Insurance numberNINO validator