🏦 IBAN Validator
Checks whether an IBAN passes the standard mod-97 checksum used by every issuing bank. This confirms the number is well-formed — it does not confirm the account actually exists. Not financial advice.
The mod-97 check, step by step
Spaces are stripped, the first four characters are moved to the end, then every letter becomes a two-digit number - A is 10 through to Z is 35 - and the whole thing is divided by 97. A valid IBAN always leaves a remainder of exactly 1:
GB82 WEST 1234 5698 7654 32
-> WEST12345698765432GB82
-> 3214282912345698765432161182
-> mod 97 = 1 validThat number is far too long for ordinary arithmetic, so the remainder is taken nine digits at a time. The length is checked first, against a built-in table of 67 countries: 22 for the UK and Germany, 27 for France, 18 for the Netherlands, 15 for Norway, 31 for Malta.
What a green tick does and does not prove
- It proves the number is well-formed - not that the account exists, that it is open, or that it belongs to the person you are paying.
- The national part is not parsed. A country's own bank and branch code layout is not checked, and there is no BIC or bank-name lookup.
- A country code outside the table still gets the checksum, just without the length check.
Frequently asked questions
What mistakes does the IBAN checksum catch?
All single mistyped characters and all swaps of two adjacent ones, which is what the two check digits were designed for. A random invalid number still has roughly a 1 in 97 chance of slipping through, so the check is a filter, not a guarantee.
My IBAN is valid - will the payment definitely arrive?
Not necessarily. The number can be perfectly formed and belong to a closed account, or to someone other than your intended payee. Banks increasingly run a separate payee-name check for exactly this reason.
Why is my IBAN rejected for the wrong length?
Every country has one fixed length, and yours did not match it. The usual causes are a missing character, a national account number pasted without its country prefix and check digits, or letters that were actually zeros and ones read as O and I.