Validator
Polish NIP validator
A mistyped NIP can be difficult to spot manually. This validator checks ten digits, the format published in the KSeF SDK and the checksum. It does not look up a business, establish NIP issuance or replace a VAT-register check. “Structure passes” means only that these technical checks passed.
Validator
Enter data
One NIP. Spaces and ordinary hyphens are accepted; a PL prefix and other characters are not discarded. Fields marked with an asterisk are required.
Technical check, not official verification. We do not check issuance, ownership, VAT status or PESEL reservation. Numbers are not sent to registers.
How to use the calculator
- Enter one number and select “Check”.
- Read the format, checksum and any date checks separately. Do not treat the result as proof of issuance.
- Report problems using test data rather than sending a real identifier.
Calculation details
Formula and calculation method
Multiply the first nine digits by weights 6, 5, 7, 2, 3, 4, 5, 6, 7. The sum modulo 11 must equal digit ten. Remainder 10 cannot be a check digit.
Worked example
For technical example 1010000002, the weighted sum of the first nine digits is 13. Remainder 13 modulo 11 is 2, matching the last digit. Changing it to 3 fails the checksum. This example does not establish that the number is unissued.
Limitations
- Passing structure does not establish issuance, current status, ownership or absence of misuse. Incorrect numbers are not automatically repaired.
- The SDK format requires a first digit from 1–9 and at least one nonzero second or third digit. Tax-office prefix allocation and EU VAT status in VIES are not checked.
Sources
- Ministry of Finance / CIRFMF — KSeF SDK NIP checksum (code reviewed 30 September 2026)
- Ministry of Finance / CIRFMF — KSeF SDK NIP format (code reviewed 30 September 2026)
- Ministry of Finance — structural identifier checks, not issuance verification
- Polish tax administration — using the VAT register (a separate check)
Engine version: 1.0.0 · Last reviewed: 30 September 2026
Frequently asked questions
Does a passing NIP definitely exist in a register?
No. This is a technical check without register access or ownership verification.
Can I enter spaces and hyphens?
Yes. Whitespace and ordinary hyphens are removed. Letters, a PL prefix, dots and non-ASCII lookalike digits are not accepted.
Are my identifiers saved or sent?
No. Form data and results are processed in your browser without being added to the URL, persistent storage or analytics, and without register requests. Copying and printing are deliberate actions. Keep your device and clipboard secure.