IBAN Calculator

Every IBAN is built from the same three parts: a two-letter ISO country code, two check digits, and the BBAN — the Basic Bank Account Number whose length and internal layout each country defines for itself. Take GB29 NWBK 6016 1331 9268 19: GB identifies the United Kingdom, 29 are the check digits, and NWBK 6016 1331 9268 19 is the BBAN holding the bank identifier, sort code and account number.

When you paste an IBAN into the validator, it removes the spaces, converts everything to uppercase and splits the string at exactly these boundaries, showing the country code, check digits, BBAN and total character count. The format check then tests the generic IBAN pattern — two letters, two digits, then letters or digits — using the regular expression ^[A-Z]{2}[0-9]{2}[A-Z0-9]+$, while the length check compares the total against the official length registered for that country.

The two check digits protect the whole IBAN using the mod-97 technique from ISO 13616, and this calculator implements it exactly as the standard prescribes: move the first four characters (country code plus check digits) to the end of the string, replace every letter with a number — A=10, B=11, and so on up to Z=35 — and treat the result as one long integer. The IBAN is valid only when that integer divided by 97 leaves a remainder of exactly 1.

Here is the example IBAN GB29 NWBK 6016 1331 9268 19 run through the algorithm. Rearranging gives NWBK60161331926819GB29; converting the letters (N=23, W=32, B=11, K=20, G=16) produces the integer 2332112060161331926819161129; and 2332112060161331926819161129 mod 97 equals 1, so the IBAN passes. Alter any single character and the remainder jumps away from 1 — that is how the checksum catches typos before a payment is sent.

The generator applies the same arithmetic in reverse. It assembles the country code, two placeholder zeros and the BBAN, computes 98 minus the mod-97 remainder of that string, and writes the result in as the real check digits — the standard construction that guarantees the finished IBAN passes validation. For United Kingdom accounts the BBAN is built from the sort code followed by the account number padded to eight digits.

The IBAN is the address of a bank account in the international payment system. Inside SEPA — the Single Euro Payments Area, which covers the EU plus countries such as the United Kingdom, Switzerland, Norway and Iceland — an IBAN is all you need to send or receive a euro credit transfer or direct debit, and banks check it electronically before the payment leaves your account. On SWIFT payments outside SEPA the IBAN identifies the account while a separate BIC identifies the bank itself. The formatted output groups the IBAN into blocks of four characters, the convention used on bank statements and in online banking, and one click copies it to the clipboard.

Because every country fixes its own IBAN length, the number of characters is itself a strong validation signal — the calculator compares your input against the registered length for all 34 supported countries:

A valid checksum is not proof that an account exists. Mod-97 only catches typing errors: the account may be closed, renumbered, or — in the classic invoice-fraud scenario — belong to an attacker who has just swapped the beneficiary IBAN in a supplier's email. Always reconfirm an IBAN against a bank statement or an independently verified contact before sending money, and treat any last-minute IBAN change as a red flag.

This calculator runs entirely in your browser: nothing you type is transmitted to a server or stored anywhere, so you can safely check your own account details before handing them to a payer. Two small conveniences of the input handling: spaces are ignored automatically and lowercase letters are converted to uppercase, so pasted IBANs work as-is.

One caveat about the generator: it builds a correctly structured IBAN from the details you enter, padding the BBAN to the standard length for the chosen country, but it cannot know whether that account actually exists at the bank. Use it to format details you already hold, not to invent account numbers.