A NIP (Numer Identyfikacji Podatkowej) is the 10-digit tax identification number assigned to every Polish business and many individuals by the tax authority. Before you trust a NIP on an invoice, a JPK file, or a ZUS filing, you can confirm it is internally well-formed using the official check-digit rule. This free validator runs that exact check in your browser.
How it works
The NIP uses a weighted modulo-11 check digit:
- Strip dashes and spaces so you have 10 digits.
- Multiply the first 9 digits by the positional weights: 6, 5, 7, 2, 3, 4, 5, 6, 7.
- Add the 9 products together.
- Compute
sum mod 11. - If the remainder is 10, the NIP is invalid (no single check digit can equal 10). Otherwise the remainder must equal the 10th digit.
The tool shows you the weighted sum and the sum mod 11 value so you can see precisely why a number passed or failed.
Example
Validate 526-104-21-44 → digits 5 2 6 1 0 4 2 1 4 4.
Apply the weights to the first nine digits:
(5×6) + (2×5) + (6×7) + (1×2) + (0×3) + (4×4) + (2×5) + (1×6) + (4×7) = 144.
144 mod 11 = 1 — but the provided check digit is 4, so this example would fail. A correct NIP is one where the computed remainder matches the final digit exactly.
Notes
A valid check digit confirms the number is well-formed, not that the taxpayer is registered for VAT. To confirm a counterparty is active, use the Polish Biała lista podatników VAT or the EU VIES service. Everything here runs locally — your NIP never leaves your device.