IBAN Validator
Validate an International Bank Account Number using the mod-97 checksum.
How IBAN validation works
An IBAN is validated by moving the first four characters to the end, converting letters to numbers (A=10 ... Z=35), and checking that the resulting number is divisible by 97.
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How this tool works
An IBAN is the account identifier used across the euro area and around seventy other countries, and it is defined in ISO 13616. It is up to 34 characters, begins with a two-letter country code and two check digits, and the rest is the national account number. The whole string is validated as one number rather than field by field, which is what makes the check digits work.
Validation runs in four stages. The country code must be one of the recognised ones, the check digits must be two digits, the national part must be alphanumeric and of the right length for that country, and the whole thing must pass the ISO 7064 mod 97-10 checksum. The checksum is the one that matters, and it is computed by moving the first four characters to the end, converting letters to their numeric positions, and checking that the resulting integer is a multiple of 97.
Worked example
| Step | Value |
|---|---|
| IBAN | GB82 WEST 1234 5698 7654 32 |
| Moved to the end | WEST12345698765432GB82 |
| Letters as numbers | 3214282912345698765432 17 18 29 |
| Modulo 97 | 1 |
| Result | Valid, the remainder is 1, which is the expected value |
A valid IBAN says the string is well formed. It says nothing about whether the account exists or who holds it.
When to use it
- Validate an IBAN before a payment or a refund
- Catch a transposed character in a manually keyed IBAN
- Confirm that the country code matches the country the payment is expected to come from
- Reconcile a set of account records against a bank file
Frequently asked questions
What is an IBAN?
The International Bank Account Number: a country-coded account identifier used across most of Europe and around seventy other countries, defined in ISO 13616. It is up to 34 characters and includes its own check digits.
How is an IBAN validated?
Four stages: a recognised country code, two numeric check digits, a national part of the right length and alphabet for that country, and the ISO 7064 mod 97-10 checksum over the whole string.
Does a valid IBAN mean the account exists?
No. The checksum proves the string is internally consistent. Whether the account is open, who holds it and what currency it holds are questions only the bank can answer.
What is the mod 97-10 method?
The ISO 7064 checksum used by IBANs. You move the first four characters to the end, turn each letter into its position in the alphabet plus ten, and check that the resulting number leaves a remainder of 1 when divided by 97.
Why do IBANs contain letters?
Because the country codes and the national account numbers are written as text so that the identifier is readable and so that the checksum can be computed over the characters rather than over a fixed-width binary field.
Can a valid IBAN still be rejected by a payment?
Yes. A structurally valid IBAN can fail on a name mismatch, a missing mandate, a currency mismatch or a closed account. The checksum is the first filter, not the last one.