How to Verify an IBAN — Structure, Formula & Free Checker

An IBAN (International Bank Account Number) is a standardized alphanumeric sequence that identifies an individual bank account at a specific financial institution in a specific country. Originally formulated by the European Committee for Banking Standards (ECBS) and later adopted globally under ISO 13616, it is the cornerstone of automated payments across SEPA and beyond. Every IBAN consists of up to 34 alphanumeric characters structured into three mandatory parts: 1. Country Code (2 letters): The ISO 3166-1 alpha-2 code indicating the country where the account resides (e.g., DE for Germany, FR for France, ES for Spain). 2. Check Digits (2 numbers): A mathematically derived two-digit security checksum (positions 3 and 4) computed using the MOD-97 algorithm. This ensures that any typo, omitted digit, or transposed character is instantly caught before payment execution. 3. Basic Bank Account Number (BBAN) (up to 30 alphanumeric characters): Country-specific format containing the national bank identifier (bank code, routing code, or BLZ), branch sorting code, and individual customer account number.

The total length and formatting of the BBAN component depend on national banking regulations. Below is a detailed breakdown of IBAN structures across key European target countries and international banking centers:

Financial software and banking payment gateways validate an IBAN using the ISO 7064 MOD 97-10 check digit algorithm. This calculation operates in four deterministic steps: Step 1: Rearrange the characters Move the first four characters of the IBAN (the two-letter country code and the two check digits) to the very end of the string. Step 2: Convert letters to numbers Replace every letter in the string with its two-digit numerical equivalent, where A = 10, B = 11, C = 12 ... through Z = 35. Step 3: Compute the modulus 97 remainder Interpret the resulting long numerical sequence as an integer and compute its remainder when divided by 97 (using modular arithmetic: sequence MOD 97). Step 4: Verify the checksum If the remainder equals exactly 1, the IBAN checksum is mathematically valid. If the remainder is anything other than 1, the number contains an error. ════════════════════════════════════════════════════════ FULL WORKED EXAMPLE: Target IBAN: DE89370400440532013000 Step 1 (Move first 4 characters to end): 370400440532013000DE89 Step 2 (Convert D → 13, E → 14): 370400440532013000131489 Step 3 (MOD 97 calculation): 370400440532013000131489 MOD 97 = 1 ✓ Result: Valid IBAN. The check digits '89' accurately secure this account. ════════════════════════════════════════════════════════

Payment delays, rejected wire transfers, and expensive bank bounce fees frequently stem from small clerical oversights. When entering or collecting account numbers, beware of these common pitfalls: 1. Wrong Country Code: Mistyping the leading two letters (e.g. typing DO instead of DE, or FS instead of FR). Country codes must strictly follow ISO 3166-1. 2. Incorrect Number of Digits: Each country has an immutable character length. A German IBAN must always be 22 characters; a French IBAN must always be 27 characters. Missing trailing or leading zeros is the single most frequent cause of invalid length. 3. Spaces and Formatting Characters: While printed statements use groups of four characters (e.g. DE89 3704 0044 0532 0130 00) for human readability, digital processing requires a clean string without hyphens, dots, or hidden non-breaking spaces. 4. Typos in Account Number: Transposing two adjacent digits (e.g. typing 0523 instead of 0532). The MOD-97 algorithm detects 99.99% of single-character alterations and adjacent character swaps, immediately flagging them as invalid.