What is the format of a Polish IBAN?

A Polish IBAN is always exactly 28 characters: the two-letter country code "PL", two check digits, then a 24-digit BBAN (Basic Bank Account Number). The BBAN encodes the bank identifier (3 digits), branch code (4 digits), NRB check digit (1 digit), and the 16-digit account number. Unlike many European IBANs, the Polish BBAN contains no letters — every character after "PL" is a digit.

How does the MOD-97 checksum work?

The ISO 7064 MOD-97-10 algorithm rearranges the IBAN by moving the first four characters (country code + check digits) to the end, then replaces every letter with its numeric equivalent (A=10, B=11 ... Z=35). The resulting digit string is divided by 97 using modular arithmetic. A valid IBAN always gives a remainder of exactly 1. Because the number can be hundreds of digits long, the calculation is folded digit-by-digit so no floating-point overflow occurs — all arithmetic stays within safe integer range.

What is the difference between an IBAN and an NRB in Poland?

NRB (Numer Rachunku Bankowego) is the domestic 26-digit Polish account number standard introduced before IBAN. A Polish IBAN is simply "PL" + 2 check digits prepended to those 26 digits, giving 28 characters total. When paying within Poland, banks accept both formats; for cross-border SEPA transfers the full IBAN starting with PL is required.

Does this validator confirm the account actually exists?

No. Structural validation (correct length, all-numeric BBAN, passing MOD-97 checksum) cannot tell you whether the account is open, the owner is who they claim to be, or that the bank code is still active. Only the account-holding bank can verify existence. Always confirm new payee details directly with the recipient through a trusted channel before transferring funds.

Which Polish banks are recognised in the lookup table?

The tool maps the leading three-digit bank code against a reference table of Polish bank identifiers maintained by the National Bank of Poland (NBP) and the Polish Bank Association. Common institutions — PKO Bank Polski, mBank, ING Bank Slaski, Santander Bank Polska, Bank Millennium, Pekao SA, Alior Bank, BNP Paribas Polska, and many others — are included. If the code shows "Unknown bank" the account may still be valid; the identifier may belong to a cooperative bank, a foreign branch, or a newer entrant not yet in the reference data.

Is my account number data private?

Completely. The entire validation — checksum arithmetic, bank-code lookup, BBAN decoding — runs inside your browser using JavaScript. No IBAN, no bank code, and no personal data is ever transmitted to a server. You can disconnect from the internet and the tool still works.

Polish IBAN Validator (NRB)

Polish IBANs follow a precise 28-character structure defined by ISO 13616 and administered by the National Bank of Poland (NBP). Every number begins with the two-letter country code PL, followed by two check digits and a 24-digit BBAN (Basic Bank Account Number). Unlike the IBANs of many other countries, Poland’s BBAN is entirely numeric — no letters appear after the PL prefix — making it straightforward to validate but easy to enter incorrectly when transcribing by hand.

This validator checks three things in sequence. First, it confirms the structural requirements: the input must be exactly 28 characters, must start with PL, and every character after PL must be a digit. Second, it runs the full ISO 7064 MOD-97-10 checksum so you can catch single-digit transposition errors that would otherwise pass a visual check. Third, it decodes the BBAN into its four components — bank code, branch code, NRB check digit, and account number — and cross-references the bank code against a reference table of Polish financial institutions so you can quickly confirm you are sending to the right institution.

How it works

The MOD-97 algorithm works by rearranging the IBAN: the first four characters (PL + two check digits) move to the end, and any letters are replaced by two-digit numbers (P becomes 25, L becomes 21). The result is a long numeric string. Dividing that number by 97 and checking that the remainder equals 1 is the validity test. Because the string can be 30+ digits long, the division is performed digit-by-digit using modular folding — each step is remainder = (remainder * 10 + nextDigit) % 97 — which keeps every intermediate value well within a 32-bit integer.

The BBAN decodes as follows using the Polish NRB standard:

Position (within BBAN)	Length	Meaning
1–3	3 digits	Bank identifier
4–7	4 digits	Branch / settlement unit
8	1 digit	NRB check digit
9–24	16 digits	Customer account number

The bank identifier maps to a name in the reference table; if the code is not found, the account may still be valid — cooperative banks and newer entrants sometimes use identifiers not yet in public reference data.

Worked example

Take the commonly cited test IBAN PL 61 1090 1014 0000 0712 1981 2874.

Strip spaces: PL61109010140000071219812874 (28 characters). Move PL61 to the end: 109010140000071219812874PL61. Replace P with 25 and L with 21: 10901014000007121981287425 61. Fold that digit string modulo 97 and the remainder is exactly 1 — valid.

Decoding the BBAN 109010140000071219812874:

Bank code: 109 — Santander Bank Polska
Branch: 1014
NRB check digit: 0
Account: 0000071219812874

The formatted print form is PL 61 1090 1014 0000 0712 1981 2874, which you can copy with the button below the result table.

Every computation runs locally in your browser. Paste an IBAN in any format — with or without spaces — and the result appears instantly.