How is an IBAN checksum calculated?

Move the first four characters to the end, replace each letter with a number (A = 10 … Z = 35), and treat the result as a large integer. A valid IBAN leaves a remainder of exactly 1 when divided by 97.

Does a valid IBAN mean the account exists?

No. The checksum proves the number is well-formed. Whether the account exists and belongs to who you think requires confirmation from the bank — which is why invoice-redirection fraud works with perfectly valid IBANs.

What is the difference between IBAN and BIC?

The IBAN identifies the account; the BIC (or SWIFT code) identifies the bank. Many transfers within SEPA now need only the IBAN.

Why do IBAN lengths differ by country?

Because each country kept its existing domestic account format as the BBAN and wrapped it in the IBAN structure. Lengths are fixed per country and are themselves a validity check.

IBAN Decoder & Validator

Validate an IBAN's checksum and read its country, bank and account parts.

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RAW INPUT

DECODED

Output appears here as you type — decoded on your device.

Input is processed on your device. Nothing you paste is sent anywhere.

What is the IBAN Decoder & Validator?

An IBAN decoder validates an International Bank Account Number using its mod-97 checksum and splits it into its components — the country code, the two check digits, and the country-specific bank and account identifiers.

An IBAN starts with a two-letter ISO country code and two check digits, followed by a Basic Bank Account Number whose length and layout are defined by each country. A German IBAN is 22 characters, a UK one 22, a French one 27, a Maltese one 31 — the length itself is a validity check, since each country's is fixed.

The checksum is a mod-97 calculation: move the first four characters to the end, convert letters to numbers (A = 10 through Z = 35), and the resulting integer must leave a remainder of 1 when divided by 97. It catches every single-character error and essentially all transpositions, which is precisely why IBANs were introduced — a mistyped account number sends money somewhere real and unrecoverable.

Validation confirms the number is well-formed, not that the account exists. That distinction matters in payment fraud, where a plausible IBAN in a redirected invoice will validate perfectly.

IBAN Decoder & Validator at a glance

Structure: 2-letter country + 2 check digits + BBAN
Checksum: mod-97-10 (ISO 7064) — remainder must be 1
Length: Fixed per country: 22 DE/GB, 27 FR, up to 34 max
Validates: Format only — not that the account exists

How to use the IBAN Decoder & Validator

1Paste the IBAN; spaces and lower case are handled.
2Check that the country, length and mod-97 checksum all validate.
3Read the bank and account components split out of the BBAN.

When you would reach for it

Verifying supplier bank details before setting up a payment.
Catching a transcription error in an invoice or a form submission.
Confirming which country an account belongs to from the IBAN alone.

IBAN Decoder & Validator — frequently asked questions

Last reviewed 25 July 2026 · questions or corrections: contact@decoder.tools