Validate International Bank Account Numbers with check digit verification and country format checking.
IBAN Validator determines whether an International Bank Account Number is structurally plausible for its stated country. It reads the first two letters as the country code, checks the country's required IBAN length and character pattern, and tests the two check digits using the IBAN MOD 97-10 calculation. A valid result means the identifier is internally consistent. It does not mean the account exists, remains open, accepts a particular payment, or belongs to the intended recipient. That distinction is the most important limitation when interpreting the result.
A concrete input and expected output from the current implementation.
Input
GB82WEST12345698765432
Expected output
Valid IBAN
Moving GB82 to the end and converting letters to numbers, with A = 10 through Z = 35, produces 3214282912345698765432161182. This number leaves remainder 1 when divided by 97, and the 22-character value also matches the GB IBAN structure.
An IBAN contains a two-letter country code, two decimal check digits, and a country-defined Basic Bank Account Number, or BBAN. The country code determines the required total length and the permitted letter and digit positions. The validator compares the entered identifier with that country's structure, so a checksum-consistent string can still fail when its length or character layout is wrong.
For check digit verification, the first four characters are moved to the end of the IBAN. Letters are replaced by decimal values from A = 10 through Z = 35, creating one long integer. The validator calculates that integer modulo 97. A correctly formed IBAN must produce a remainder of 1; any other remainder fails the check.
No. Validation establishes that the identifier follows the stated country's IBAN structure and passes its mathematical check. It cannot confirm account ownership, current account status, supported currencies, payment-rail eligibility, or whether the recipient supplied the intended account. Confirm unfamiliar or changed payment instructions through a trusted channel before sending funds.
Length is only one test. The letters and digits must occupy the positions required by that country's BBAN structure, and the complete identifier must produce the required modulo 97 remainder. A single mistyped character usually changes that remainder. The validator can detect the inconsistency, but it cannot determine which character should replace the incorrect one.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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