IBAN Check Digit Calculator

Calculate correct check digits using the MOD-97 algorithm or verify existing IBANs

Calculate Check Digits

Select the country

Expected length: 18 characters

Format: 8n 10n
Example: DE89 3704 0044 0532 0130 00

About MOD-97 Algorithm

The MOD-97 algorithm is used to calculate and verify IBAN check digits according to ISO 13616 standard.

How it works:
  1. Replace the check digits with "00" in the IBAN
  2. Move the first 4 characters to the end
  3. Replace each letter with its numeric equivalent (A=10, B=11, ..., Z=35)
  4. Calculate the remainder when divided by 97
  5. Subtract the remainder from 98 to get the check digits
Verification:

To verify an IBAN, perform the same calculation. If the final MOD 97 result equals 1, the IBAN is valid.

💡 Why MOD-97?
The MOD-97 algorithm can detect up to 99% of transcription errors, including single digit errors, transposition of adjacent digits, and most other common mistakes.

How to Calculate IBAN Check Digits

  1. Enter the country code (2 letters)
  2. Input the BBAN (Basic Bank Account Number)
  3. Click "Calculate Check Digits" to generate the correct digits
  4. Alternatively, enter a complete IBAN to verify its check digits
  5. View step-by-step MOD-97 calculation breakdown

Why Use Our Check Digit Calculator?

  • 100% Free: No hidden costs or subscriptions
  • Educational: Understand the MOD-97 algorithm with step-by-step explanations
  • Instant Results: Calculate or verify check digits immediately
  • Developer-Friendly: Learn implementation details for your own validation
  • Debugging Tool: Troubleshoot IBAN generation or validation issues
  • Accurate: Uses the official MOD-97 algorithm per ISO 13616

Features of Our Calculator

  • Calculate Mode: Generate check digits from country code and BBAN
  • Verify Mode: Validate existing IBAN check digits
  • Step-by-Step Breakdown: See each calculation step explained
  • MOD-97 Algorithm: Official ISO 13616 standard implementation
  • Error Detection: Identifies common mistakes in manual IBAN entry
  • Educational Tool: Perfect for learning international banking standards

Understanding the MOD-97 Algorithm

The MOD-97 algorithm is the mathematical foundation of IBAN validation. It ensures that IBANs are entered correctly and detects most transcription errors. Here's how it works: First, move the first 4 characters (country code + check digits) to the end of the IBAN. Second, replace each letter with its numeric equivalent (A=10, B=11, ... Z=35). Third, treat the resulting number as a single integer and calculate the remainder when divided by 97. For a valid IBAN, this remainder must equal 1. For example, GB82WEST12345698765432 becomes WEST12345698765432GB82. Converting letters gives 3214282919123456987654321611820. Dividing by 97 gives remainder 1—valid! If generating check digits, use placeholder 00, calculate MOD-97, then subtract result from 98. This algorithm catches 98% of all data entry errors.

Common Use Cases for Check Digit Calculation

  • IBAN Generation: Create valid IBANs from existing bank account numbers.
  • Validation Testing: Verify your IBAN validation implementation works correctly.
  • Educational Purposes: Teach banking standards and validation algorithms.
  • Debugging: Troubleshoot why an IBAN fails validation.
  • Data Migration: Generate IBANs when converting from legacy account formats.
  • Manual Entry Verification: Check if manually-entered IBANs are valid.

Privacy & Security

All check digit calculations are performed entirely in your browser. No IBAN data is sent to our servers, ensuring complete privacy. The calculator is purely educational and should not be used to generate real IBANs for financial transactions without proper authorization from banking institutions.