IBAN check, without sending the account number anywhere
Validate an IBAN’s length and check digits in your browser before a payment goes out, and read the sort code and account number back out of a UK one.
- Takes
- An IBAN, with or without spaces
- Upload
- None
- Account
- Not required
- Runs
- In your browser
Spaces and hyphens are ignored. It is checked in this tab and never transmitted — which matters, because this is a bank detail.
The check
An IBAN is a country code, two check digits, and the domestic account details padded to a fixed length. The validation is a rearrangement and one division: move the first four characters to the end, replace each letter with a number — A is 10, Z is 35 — and the result taken modulo 97 must be exactly 1.
Length is checked first, because it is per-country and a wrong one is a faster answer than a failed checksum. A UK IBAN is 22 characters, a German one 22, a French one 27, a Maltese one 31. If the length is wrong, a character is missing or extra and there is no point running the arithmetic.
The two failures are worth separating, which is why this reports three states rather than two. Not the right shape means the length or the character set is wrong — usually a truncated paste. Fails the check means it is the right length and the right shape, but the check digits disagree with the rest, which is a single mistyped character. Most often that is a digit, occasionally a capital O where a zero was meant.
The sort code is in there
A UK IBAN contains the details you already recognise. After the country code and check digits come four letters for the bank, six digits of sort code, and eight digits of account number. When you paste a GB IBAN this tool reads them back out, which is the quickest way to confirm that the international number a supplier sent you points at the domestic account you were expecting.
What it does not prove
The checksum catches a mistyped character. That is the mistake it is for, and it is the one that costs you a returned payment and a fee.
It cannot tell you the account is open, and it cannot tell you who it belongs to. A perfectly well-formed IBAN belonging to the wrong person is still the wrong person — which is the mechanism behind most invoice redirection fraud, and no amount of arithmetic will catch it. Verifying that the payee is who they claim to be is a phone call to a number you already had, not a checksum.
Why it runs here
Every other IBAN checker asks you to send a bank account number to a server you know nothing about, to run a calculation that takes microseconds. This one runs in your browser. Nothing is transmitted, nothing is stored, and closing the tab is the whole of the cleanup.
Early access
This is one file. Databoat does the rest.
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