Polish NIP validator - check a tax identification number

NIP (Numer Identyfikacji Podatkowej) is the Polish tax identification number. Every company, partnership and sole trader in Poland has one, and so does any business registered for VAT. It appears on every invoice, in contracts, in the KSeF e-invoicing system and in tax returns. Private individuals who do not run a business and are not VAT payers normally use their PESEL number in dealings with the tax office instead.

If you work with Polish suppliers or clients, or you set up a sole proprietorship (jednoosobowa działalność gospodarcza) in Poland, you will see NIP numbers constantly. A quick check before issuing an invoice saves you a correcting invoice later.

A NIP has 10 digits. The first nine are multiplied by the weights 6, 5, 7, 2, 3, 4, 5, 6, 7, the products are added up and the sum is divided by 11. The remainder must equal the tenth, final digit. If the remainder is 10, the number is invalid - such combinations are never issued.

Example for 526-025-02-74: 5·6 + 2·5 + 6·7 + 0·2 + 2·3 + 5·4 + 0·5 + 2·6 + 7·7 = 30 + 10 + 42 + 0 + 6 + 20 + 0 + 12 + 49 = 169. 169 mod 11 = 4, and the last digit is 4, so the number is valid.

• 5260250274 - digits only, used in accounting software, JPK files and KSeF,
• 526-025-02-74 or 526-02-50-274 - two dash layouts that both appear on documents and mean the same number,
• PL5260250274 - the EU VAT identification number used for intra-EU transactions (country code plus NIP).

The validator strips dashes, spaces, dots and the PL prefix before checking. The first three digits are the code of the tax office that originally issued the number; a NIP does not change when a company moves, so the code may not match the current address.

A correct checksum only proves the number is well-formed - for example, that it contains no typo. It does not confirm that the company exists or that it is an active VAT payer. For that, use the official registers: the White List of VAT taxpayers (Wykaz podatników VAT) run by the Head of the National Revenue Administration, CEIDG for sole traders and KRS for companies. For cross-border B2B sales, check the EU VAT number in the European Commission VIES system. If you also need to verify a statistical number or a bank account, use the REGON validator or the IBAN validator.