Austrian IBAN Validator

Austrian IBANs follow a strict 20-character format defined by the SWIFT IBAN Registry and enforced under ISO 13616. Whether you are wiring money via online banking, onboarding a supplier in your accounts-payable system, or double-checking a customer’s bank details before a SEPA Direct Debit, a single transposed digit can misdirect the payment and trigger costly correction fees. This validator catches those errors instantly — no login, no network request, no data ever leaves your device.

How Austrian IBAN validation works

An Austrian IBAN always starts with AT followed by two check digits, a five-digit Bankleitzahl (BLZ) and an eleven-digit account number, giving twenty characters in total:

AT  kk  bbbbb  bbbbbbbbbbb
^   ^   ^      ^
|   |   |      account number (11 digits)
|   |   Bankleitzahl / BLZ (5 digits)
|   check digits (2)
country code

The validator runs three checks in sequence:

1. Length check — the stripped input must be exactly 20 characters. Austria is one of the shorter IBANs in Europe; if yours is 16 or 22 characters you likely have a different country’s IBAN or extra/missing digits in the account number.

2. BBAN numeric check — positions 5 to 20 (the BLZ and account number combined) must contain only digits 0–9. No letters are permitted inside the Austrian BBAN.

3. ISO 7064 MOD-97-10 checksum — the heart of IBAN validation. The algorithm rearranges the IBAN by moving the first four characters (ATkk) to the end, then replaces every letter with its numeric code (A becomes 10, T becomes 29, and so on). The resulting digit string is divided by 97; the result is valid only when the remainder equals 1. Because the number can be up to 30 digits long the tool folds the computation progressively to stay within JavaScript’s safe integer range.

Worked example

Take the IBAN AT61 1904 3002 3457 3201 — a well-known test value published in the SWIFT registry:

• Country code: AT
• Check digits: 61
• BLZ: 19043
• Account number: 00234573201

MOD-97 check:

Rearrange by moving AT61 to the end: 190430023457320110293361

Expand letters (A=10, T=29): 190430023457320110293361 (No letters in this BBAN, so the string is already numeric.)

Divide by 97: remainder = 1 — checksum passes.

The formatted canonical output is AT61 1904 3002 3457 3201. Common mistakes include copying only the 11-digit account number from your passbook without the BLZ prefix, or accidentally including an Austrian Bankverbindung reference code that is not part of the IBAN itself. Both are caught immediately by the length check.

Austrian bank BLZ reference (selected)

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