What is the format of an Irish IBAN?

An Irish IBAN is always 22 characters: the 2-letter country code IE, 2 numeric check digits, a 4-letter bank identifier code (e.g. AIBK for AIB or BOFI for Bank of Ireland), a 6-digit sort code and an 8-digit account number. Spaces are purely cosmetic and are not part of the stored value.

How does the MOD-97 checksum work?

The four-step ISO 7064 procedure is: (1) move the first four characters (IE + check digits) to the end of the string; (2) replace every letter with its two-digit numeric equivalent (A=10, B=11 up to Z=35); (3) interpret the whole result as one large integer; (4) divide by 97 and keep the remainder. A remainder of 1 means the IBAN is structurally valid. The tool folds the division progressively over the digit string so no overflow can occur.

Does a valid result mean the account actually exists?

No. The tool checks structural correctness only — country code, length, BBAN character types and the MOD-97 arithmetic. It cannot query any bank register or Revenue database. A structurally valid IBAN may belong to a closed account or may never have been issued. Only the receiving bank can confirm whether an account is live and open.

What is the BBAN and why does Ireland use 4 letters at the start?

BBAN stands for Basic Bank Account Number — the country-specific portion that follows the two check digits. Ireland's BBAN is 18 characters long: four uppercase letters identify the bank (derived from the institution's SWIFT BIC code), then six digits give the sort code (routing the payment to a branch) and eight digits are the customer account number. The letter block is unique to Ireland among SEPA countries; most other countries use entirely numeric BBANs.

Which banks are in scope for Irish IBANs?

Any bank authorised to operate within SEPA (the Single Euro Payments Area) and holding an IE country code can issue Irish IBANs. Common codes include AIBK (AIB), BOFI (Bank of Ireland), IPBS (Permanent TSB) and ULSB (Ulster Bank Ireland). The tool recognises several well-known codes and displays the institution name, but an unrecognised code is not itself an error — new or smaller institutions may not be in the lookup table.

Is my IBAN transmitted to any server when I use this tool?

No. Every step of the validation — character extraction, letter-to-digit conversion, modulo arithmetic and BBAN parsing — runs entirely inside your browser. No data is uploaded, logged or stored at any point. You can disconnect from the internet after the page loads and the tool will continue to work.

Irish IBAN Validator

An Irish IBAN (International Bank Account Number) is the standard way to identify an Irish bank account for SEPA credit transfers and direct debits across the 36-country Single Euro Payments Area. Ireland adopted IBANs alongside the wider eurozone as part of the SEPA migration that completed in February 2014, replacing the older combination of a six-digit sort code and eight-digit account number used in domestic transfers. Today every Irish bank account — whether held at AIB, Bank of Ireland, Permanent TSB, Ulster Bank or a digital challenger — has an IBAN that begins with the two-letter country code IE and runs to exactly 22 characters.

Typos in IBANs can redirect payments to the wrong account or cause costly returns. The ISO 7064 MOD-97-10 checksum built into every IBAN catches the vast majority of single-character errors and transpositions before a payment is even submitted. This validator runs the full algorithm locally and exposes every intermediate value — the bank code, sort code, account number and the modular remainder — so you can see exactly why an IBAN passes or fails rather than simply receiving a yes-or-no verdict.

Structure of an Irish IBAN

An Irish IBAN decomposes into four logical sections across its 22 characters:

Section	Characters	Example	Meaning
Country code	1-2	IE	ISO 3166-1 alpha-2 for Ireland
Check digits	3-4	29	MOD-97-10 integrity digits
Bank code	5-8	AIBK	Four-letter bank identifier (from SWIFT BIC)
Sort code	9-14	931152	Six-digit branch routing number
Account number	15-22	12345678	Eight-digit customer account number

The bank code is the most distinctive feature of an Irish IBAN. Unlike the purely numeric BBANs used in Germany, France or the Netherlands, Ireland encodes the bank identifier as four uppercase letters derived from the institution’s SWIFT BIC code. AIBK maps to Allied Irish Banks, BOFI to Bank of Ireland, IPBS to Permanent TSB and ULSB to Ulster Bank Ireland.

How the MOD-97 algorithm works

The ISO 7064 MOD-97-10 checksum involves four steps:

Rearrange the IBAN by moving the first four characters (country code IE plus the two check digits) to the end. An input of IE29AIBK93115212345678 becomes AIBK93115212345678IE29.
Expand letters to two-digit numbers using the mapping A=10, B=11, C=12 and so on up to Z=35. The rearranged string above becomes 10111120931152123456781814 followed by the numeric equivalents of IE and 29.
Compute the remainder of that long number divided by 97.
Check that the remainder equals exactly 1. Any other result means at least one character was mistyped.

Because the resulting integer can be hundreds of digits long, the tool folds the division progressively — processing one digit at a time and carrying only the running remainder — so there is never any floating-point overflow.

Worked example

Consider the structurally valid (but fictitious) IBAN IE29 AIBK 9311 5212 3456 78:

Clean string: IE29AIBK93115212345678
Rearranged: AIBK93115212345678IE29
Letters expanded: A=10, I=18, B=11, K=20, E=14 — giving the numeric string 10181120931152123456781814 followed by 29
This entire sequence is divided by 97; the remainder must be 1

The tool shows the sort code as 93-11-52 and the account number as 12345678. Changing even one digit — say turning the account number to 12345679 — would produce a different remainder and flag the IBAN as invalid, catching the error before a payment is submitted.

The validator runs entirely in your browser. No IBAN you enter is ever transmitted to a server, stored or logged in any way.