IBAN FAQ
Everything you need to know about International Bank Account Numbers
How is the IBAN check digit calculated?
Each IBAN contains a check digit that helps detect typing errors during entry and processing. It uses the Modulo 97 mathematical method to validate bank account information.
What is the check digit?
The check digit is a crucial component of the IBAN and consists of two digits that appear immediately after the country code. It serves for error detection and is calculated according to an internationally standardized procedure.
This check digit performs the following functions:
Error Detection
Identifies typos and transposed digits
Immediate Validation
Enables verification before a transaction is submitted
International Standardization
Based on the international ISO standard 7064
Uniqueness
Calculated individually for each account number
Required Information
For a German IBAN check digit calculation, you need:
- Country code: "DE" for Germany
- Bank code: 8 digits
- Account number: 10 digits (filled with leading zeros if shorter)
Example: We'll use bank code 10010010 (Postbank Berlin, BIC: PBNKDEFFXXX) and account number 987654321.
Step-by-Step Calculation
| # | Step | Result |
|---|---|---|
| 1 | Identify bank code | 10010010 |
| 2 | Identify account number | 0987654321 (added leading zero) |
| 3 | Combine to form BBAN | 100100100987654321 |
| 4 | Create IBAN with placeholder check digit | DE00100100100987654321 |
| 5 | Move country code and placeholder to end | 100100100987654321DE00 |
| 6 | Replace letters with numbers (D=13, E=14) | 100100100987654321131400 |
| 7 | Calculate Modulo 97 | 100100100987654321131400 mod 97 = 69 |
| 8 | Subtract from 98 | 98 - 69 = 29 |
| 9 | Final IBAN with check digit | DE29 1001 0010 0987 6543 21 |
How this helps:
This complex calculation ensures that any typo or transposition error in an IBAN will almost certainly produce an invalid check digit, allowing the error to be caught before a transaction is processed.
Modulo 97 Method Explained
The Modulo 97 method is a mathematical algorithm used in IBAN check digit calculation. The term "modulo" in mathematics refers to finding the remainder of a division.
In Modulo 97, a number is divided by 97 and the remainder of this division is determined. This method is particularly suitable for the following reasons:
- Detection of transposed digits: The method identifies transposed digits like "12" to "21"
- Robustness: Even with transmission errors of individual digits, the error is almost always detected
- International standardization: The method is applied uniformly worldwide
Calculate it automatically
Instead of calculating it manually, you can use our free IBAN Calculator to instantly generate and validate IBANs.
Our calculator handles the complex calculation for you and offers the following advantages:
- Instant IBAN calculation from bank code and account number
- Validation of existing IBANs for correctness
- Support for all German bank codes
- Simple and user-friendly interface
Ready to Get Started?
Use IBANTEST for precise IBAN validation and calculation – reliable and user-friendly.