Check a Polish NIP
Before issuing an invoice in KSeF, check that the buyer's NIP is valid and the company is an active VAT payer. An invoice with a wrong NIP reaches KSeF, but not your customer.
How we check
- Checksum: each of the first nine digits is multiplied by the weights 6, 5, 7, 2, 3, 4, 5, 6, 7. The sum modulo 11 must equal the last digit. This catches most typos.
- White list: the request goes from your browser straight to the public Ministry of Finance API. We do not store the numbers you enter.
- "Czynny" means an active VAT payer. An invoice to a company marked "Zwolniony" (exempt) still goes through KSeF.