IBAN Calculator — Compute Check Digits
Use this calculator to compute IBAN check digits from a country code and domestic account details. Enter a country, type the BBAN (domestic bank + account number), and we'll calculate the correct check digits using the MOD-97 algorithm.
Calculate IBAN Check Digits
How the IBAN Calculator Works
The calculator follows the official ISO 13616 algorithm for computing IBAN check digits:
- Assemble: Take the country code + "00" (placeholder check digits) + BBAN (domestic account details)
- Rearrange: Move the first 4 characters (country code + "00") to the end of the string
- Convert: Replace each letter with its numeric value (A=10, B=11, ..., Z=35)
- Divide: Interpret the result as a single large integer and compute remainder modulo 97
- Finalise: Check digits = 98 − remainder (zero-padded to 2 digits)
Why Would You Need an IBAN Calculator?
- Verify your IBAN: If you know your domestic bank code and account number, use this calculator to verify your IBAN's check digits are correct
- Understand the algorithm: See each step of the MOD-97 calculation to understand how IBAN validation works
- Educational purposes: Students and developers learning about international banking can explore the IBAN structure interactively
- Testing and QA: Validate that your payment system's IBAN generation logic produces correct check digits
IBAN Calculator vs IBAN Generator
This calculator computes check digits from your existing domestic bank details. Our IBAN Generator creates entirely random (but mathematically valid) IBANs for testing. Use the calculator when you have real bank data and need to verify the check digits; use the generator when you need test data.
Frequently Asked Questions
Can I calculate an IBAN from just a sort code and account number?
Yes! The IBAN calculator does exactly this. Enter the country, type your domestic bank code + account number (the BBAN), and we compute the correct check digits using MOD-97.
What if my calculated IBAN doesn't match the one on my bank statement?
Your bank's IBAN is the authoritative source. If there's a discrepancy, double-check that you entered the correct domestic bank code and account number. Some banks use proprietary BBAN formats that differ slightly from the standard.
Is the MOD-97 algorithm the same for all countries?
Yes. All IBAN countries use the same MOD-97 check digit algorithm (ISO 7064). The only difference between countries is the BBAN format — the length and structure of the domestic bank/account details.
Can I use this calculator for any IBAN country?
Yes! The calculator supports all 96 IBAN countries. Select your country from the dropdown, enter the BBAN in the correct format, and we'll compute the check digits.