How is the NIF control letter computed?

Take the 8-digit number, compute its remainder modulo 23, then look that remainder up in the fixed letter table TRWAGMYFPDXBNJZSQVHLCKE. The letter at that position is the valid control letter.

How is a NIE different from a NIF?

A NIE (for foreigners) starts with X, Y or Z. For the modulo-23 calculation, X is treated as 0, Y as 1 and Z as 2, then prefixed to the remaining 7 digits to form the number that is checked against the letter table.

What is the difference between DNI and NIF?

The DNI is the Spanish national ID document; the NIF is the tax identification number, which for individual Spanish citizens is the DNI number plus its control letter. The validation algorithm is identical.

Does a valid letter mean the person exists?

No. A correct control letter only confirms the identifier is internally consistent. It does not confirm the NIF/NIE is issued to a real, registered person — use official channels for that.

Is the NIF/NIE sent anywhere?

No. The calculation runs entirely in your browser. The identifier never leaves your device.

Spain NIF/NIE Validator

A Spanish NIF (Número de Identificación Fiscal) is the tax ID of Spanish citizens — the DNI number plus a single control letter. Foreign residents instead carry a NIE (Número de Identidad de Extranjero), which begins with X, Y or Z. Both use the same modulo-23 check letter. This free validator runs that exact algorithm in your browser, which is handy for HR onboarding, KYC checks and form validation.

How it works

Detect the type. If the value starts with X, Y or Z it is a NIE; if it starts with a digit it is a NIF.
Build the number. For a NIE, replace the leading letter with a digit: X → 0, Y → 1, Z → 2, then append the remaining 7 digits to get an 8-digit number. A NIF already has 8 digits.
Modulo 23. Compute number mod 23. The remainder is 0–22.
Look up the letter. Index into the fixed table TRWAGMYFPDXBNJZSQVHLCKE. The letter at that position is the correct control letter.
Compare. The NIF/NIE is valid if the computed letter equals the supplied final letter (the letters I, O, U and Ñ are intentionally excluded from the table).

Example

Validate 12345678Z: 12345678 mod 23 = 14. The 14th character (0-indexed) of TRWAGMYFPDXBNJZSQVHLCKE is Z, which matches — so the NIF is valid.

For X1234567L: X → 0, giving 01234567. 1234567 mod 23 = 10, and position 10 is L, which matches — the NIE is valid.

Notes

A correct control letter confirms the identifier is internally consistent, not that it belongs to a real, registered individual. CIF numbers (for companies) use a different algorithm and are not covered here. Everything runs locally — the identifier never leaves your browser.