This IBAN validator and formatter checks any International Bank Account Number against the official MOD-97 checksum (ISO 7064) and each country's fixed IBAN length, then reformats it into readable groups of four characters — the same layout banks print on statements.
How to use it
Paste an IBAN with or without spaces. The tool strips formatting, uppercases letters, checks the length against the expected value for that country's two-letter prefix, then runs the MOD-97 checksum. If both pass, it prints the IBAN reformatted into groups of four.
How the MOD-97 checksum works
IBAN validation moves the first four characters (country code + two check digits) to the end of the string, converts every letter to two digits (A=10 through Z=35), and treats the result as one large number. A valid IBAN always leaves a remainder of exactly 1 when that number is divided by 97 — a property mathematically guaranteed by how the two check digits were generated in the first place.
Why length matters as much as the checksum
Every IBAN country has a fixed total length — Dutch IBANs are always 18 characters, German IBANs 22, Maltese IBANs 31. A string that happens to pass the checksum but has the wrong length for its country is not a valid IBAN, so this tool checks both independently.