Check the check digit of a Polish tax ID (NIP) or business-registry number (REGON, 9 or 14 digits) - entirely locally in your browser, no upload.
Running locally on your device ...
Running locally on your device ...
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Your files never left your device
No. Everything runs in your browser - your file never leaves your device. How this is verifiable
NIP (Numer Identyfikacji Podatkowej) is Poland's 10-digit tax ID, REGON its business-registry number - either 9 digits (nationwide) or 14 digits (for a local business unit, with a second check digit over the extra 4 digits). This tool auto-detects which of the two you pasted from the digit count, and checks the matching weighted check digit.
Paste the number (spaces and dashes are ignored) and you get an instant result: the detected type (NIP, 9-digit REGON or 14-digit REGON), whether the check digit is correct, and for a NIP the rare special case where a digit sequence can never have a valid check digit at all.
The whole check runs locally in your browser in pure JavaScript - the entered number is not uploaded, not stored, and no foreign library is loaded from a CDN.
| Input formats | Text input |
|---|---|
| Output format | TXT |
| Batch processing | No |
| Processing | Locally in your browser (JavaScript) |
| File upload | None |
Limitations: This tool performs only a mathematical checksum/format check. It is not an official identity, existence, or registry verification and not a request to any authority. Any additional information derived from the number's structure is based solely on the publicly documented encoding logic of the issuing authority. Whether a tax number is actively assigned to a real, existing company can only be confirmed by an official lookup (e.g. the Polish Ministry of Finance), not by this tool.
No. The check runs entirely locally in your browser; the number never leaves your device and is not stored.
By digit count alone: 10 digits = NIP, 9 or 14 digits = REGON.
No. It only checks whether the check digit is mathematically correct - no query against a registry or any authority.
If the weighted sum of the first 9 digits leaves remainder 10, no single digit 0-9 can ever be a valid 10th check digit - the sequence can never be a valid NIP.
A second, separate check digit over the first 13 digits (so over the 9-digit base too) - additionally, that 9-digit base must itself be a valid REGON.
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