How long is an Irish IBAN?

Exactly 22 characters. The structure is IE, two check digits, a 4-letter bank identifier (the first 4 of the BIC), a 6-digit National Sort Code (NSC), and an 8-digit account number. Anything else is invalid.

Why does the Irish IBAN contain letters?

The first four BBAN characters are the bank identifier taken from the SWIFT BIC, for example AIBK for AIB or BOFI for Bank of Ireland. This is one of the few European IBANs whose BBAN intentionally includes letters.

How does the MOD-97 check work?

The first four characters are moved to the end, each letter is replaced by a number (A=10 to Z=35), and the result is divided by 97. The remainder must equal 1 for the IBAN to be structurally valid.

Does a valid result mean the account exists?

No. MOD-97 catches typos and transposed digits but cannot confirm the account is real or open. Only the bank can confirm that.

Is my IBAN sent anywhere?

No. All validation runs locally in JavaScript. Nothing is uploaded, logged, or stored, and the tool works offline once loaded.

Ireland IBAN Validator

Irish IBANs are 22 characters long and uniquely embed a four-letter bank identifier alongside the familiar 6-digit National Sort Code (NSC) and 8-digit account number. Because the IBAN mixes letters and digits, a tool that assumes a numeric BBAN will reject perfectly valid Irish accounts. This validator handles the mixed format correctly, entirely in your browser.

How it works

An Irish IBAN always begins with IE, followed by two check digits, a four-letter bank identifier (the first four characters of the bank’s BIC), a six-digit sort code, and an eight-digit account number:

IE  kk  AAAA  ssssss  aaaaaaaa
^   ^   ^     ^       account number (8 digits)
|   |   |     sort code / NSC (6 digits)
|   |   bank identifier (4 letters)
|   check digits (2)
country code

The validator runs three checks: the length must be exactly 22; the BBAN must match the pattern of 4 letters then 14 digits; and the ISO 7064 MOD-97-10 checksum must pass. For the checksum the first four characters (IEkk) are moved to the end, every letter (including the four-letter bank identifier) is replaced by its numeric code A=10 to Z=35, and the resulting long integer must leave a remainder of 1 when divided by 97. The computation is folded digit-by-digit so no big-integer library is needed.

Worked example

Take IE29 AIBK 9311 5212 3456 78: country code IE, check digits 29, bank identifier AIBK (Allied Irish Banks), sort code 931152, account 12345678. Expanding AIBK to its numeric codes and dividing the rearranged string by 97 leaves remainder 1, so the checksum passes.

Tips

The four-letter bank identifier must be uppercase letters only, never digits, so a number there is a sure sign of a mistyped or non-Irish IBAN. The 6-digit sort code is the same NSC used in domestic transfers, just embedded inside the IBAN. All figures are processed locally and never uploaded.