Poland NIP validator
How the NIP format works
- Format
- 10 digits
- Example
- 5260001246
Things to watch for
- 10 digits with a weighted mod-11 check on the final digit
- Checksum only — does not confirm the taxpayer is currently registered or active with the KAS
- A mod-11 result of 10 is never a valid check digit, so those numbers are always rejected
^[0-9]{10}$NIP (Numer Identyfikacji Podatkowej) is the tax identification number Poland’s Krajowa Administracja Skarbowa (National Revenue Administration) assigns to taxpayers — both registered businesses and individuals who need one for tax purposes. It’s a 10-digit number, often written with hyphens for readability, and it’s a separate identifier from PESEL: PESEL identifies a person for civil and social purposes, while NIP exists specifically for tax administration and can apply to a company as easily as a sole trader.
The tenth digit is a check digit, produced by multiplying each of the first 9 digits by a fixed weight, summing the results, and reducing that sum modulo 11. If that calculation ever produces 10, the number is invalid outright — the algorithm has no digit to represent it, so no real NIP ends that way. That built-in impossibility, plus the checksum’s general sensitivity to a single wrong digit, is what makes validating it worthwhile before submitting an invoice or tax form.
How this validator works
This tool checks that the input is 10 digits and reruns the weighted mod-11 calculation against the final digit, entirely in your browser with nothing sent to a server.
What a pass doesn’t tell you
A passing checksum confirms the digits are internally consistent — not that the NIP is currently registered or active, or that it belongs to the business or person you expect. Only Krajowa Administracja Skarbowa’s own taxpayer records can confirm that a specific NIP is genuinely registered and active.
Scope: this page covers NIP format and checksum validation only — not tax-authority registration status.
Content last reviewed 2026-07-22.
NIP FAQ
How is a NIP different from a PESEL?
PESEL identifies an individual person for civil and social purposes; NIP is a tax identifier that can belong to a business or an individual taxpayer. They come from different authorities and use different check-digit formulas — a valid NIP doesn't need to relate to your PESEL at all.
Why do some 10-digit numbers always fail a NIP check?
The mod-11 formula can produce 10 as its result, but there's no single digit that represents 10. Poland's algorithm treats that outcome as invalid, so no genuine NIP can ever produce it — this validator rejects those numbers the same way.
Does a valid NIP checksum mean the business is actively registered?
No. It only confirms the 10 digits are mathematically consistent. Whether a NIP is currently active, suspended, or linked to a real registered taxpayer is something only the tax authority's own records can confirm.