IBAN Calculator & Validator

The **International Bank Account Number (IBAN)** is a standardized international system for identifying bank accounts across national boundaries, originally developed by the European Committee for Banking Standards and later adopted under the **ISO 13616** international standard. The primary purpose of the IBAN is to reduce transcription errors and enhance accuracy during cross-border payments, allowing automated routing without manual checking or intervention.

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🧮 The Cryptographic MOD-97 Algorithm

At the heart of the IBAN verification system is a powerful, elegant mathematical check based on the **Modulo-97** arithmetic algorithm (defined in ISO 7064). This error-detecting mechanism ensures that if even a single character is mistyped, transposed, or omitted, the mathematical check fails, stopping faulty international wire transfers before they enter interbank clearings.

The validation process involves the following strict sequential steps:

1. Reorganization: Move the country prefix code (first two letters) and check digits (digits three and four) to the end of the IBAN. For example, the Icelandic IBAN IS890111260036662705002290 is rearranged to: 0111260036662705002290IS89.
2. Alphanumeric Substitution: Replace all letters in the string with their numeric equivalents. Each letter is mapped to a two-digit integer where A = 10, B = 11, C = 12 ... I = 18 ... S = 28 ... Z = 35. Thus, IS is replaced by 1828, converting the rearranged string into a pure number: 0111260036662705002290182889.
3. Modulo Calculation: Compute the remainder of this massive integer divided by 97. If the remainder is exactly 1, the IBAN structure is mathematically valid!

Because Modulo 97 checking is extremely comprehensive, it captures 99.9% of random keystroke errors, safeguarding global currency flows.

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🇮🇸 Structure of an Icelandic IBAN (Kennitala payload)

Every country defines a specific length and internal composition for its Basic Bank Account Number (BBAN). In Iceland, an IBAN is always exactly **26 characters** long and follows a highly specific, transparent structure that integrates local identifiers.

The 26 characters of an Icelandic IBAN are segmented into six components:

• Country Prefix (2 characters): Always IS.
• Mod-97 Check Digits (2 digits): E.g. 89, which validate the rest of the string.
• Bank Code (4 digits): Identifies the clearing bank. For example, 0111 corresponds to Landsbankinn, 0301 to Arion Bank, and 0511 to Íslandsbanki.
• Ledger Code / Category (2 digits): Known in Iceland as höfuðbók, representing the type of checking or savings account (e.g. 26).
• Account Number (6 digits): The unique account identifier within that bank (padded with leading zeros if shorter).
• National Identification Number / Kennitala (10 digits): Represents the unique 10-digit ID of the account owner. For a person, it encodes their date of birth, random identifiers, a modulus-11 check digit, and the century of birth (e.g. 270500-2290).

This high degree of structural integration makes Icelandic bank accounts extremely transparent and easy to audit programmatically, ensuring absolute safety for bank clearings coordinated through the Central Bank of Iceland (Seðlabanki Íslands).