DigiKitHow to Validate an IBAN Number
How to check whether an IBAN is valid before sending money.
Summary
A mistyped IBAN can send money to the wrong account or get the transfer rejected outright. The last two digits of an IBAN are a checksum that let you mathematically verify whether the rest of the number is correct.
Step by step
- Enter the IBAN in full, with no spaces, including the country code and check digits.
- Paste it into an IBAN validator tool, which instantly checks the format and checksum.
- A passing validation only confirms the number is mathematically well-formed, not that the account actually exists.
- For large transfers, also confirm the recipient's name through your bank's own system, even if the IBAN checks out.
How a Turkish IBAN is built
A Turkish IBAN is 26 characters long, and each part means something. It starts with the country code TR, followed by two check digits. The next five digits identify the bank, then comes a single reserved digit, and the final sixteen digits are the account number. IBAN lengths vary by country, so knowing the Turkish pattern helps you spot a number with a digit missing or added at a glance.
How the check digits work
Validation uses the "mod 97" method defined in the international IBAN standard. The first four characters are moved to the end, letters are turned into numbers (A=10, B=11 and so on), and the resulting long number is divided by 97. If the remainder is 1, the IBAN is well-formed. This catches nearly all single-digit typos and most cases where two neighbouring digits are swapped. It's tedious by hand, which is why validators exist.
Common mistakes
- Mixing up the letter O and zero, or the letter I and one. Apart from the leading TR, a Turkish IBAN contains only digits.
- Picking up an invisible trailing space or line break when copying from a PDF or chat message.
- Paying to an IBAN on an invoice without comparing it with the one that supplier has used before.
- Assuming a valid IBAN belongs to the right person.
A worked scenario
A business owner gets an email from a long-standing supplier: "Our bank account has changed, please send this month's payment to the new IBAN." The new number passes validation perfectly. Even so, she ignores the phone number in the email and calls the supplier on the number she already has. They never sent that email. Validation raised no flag, because the IBAN belonged to a real, valid account. It was just someone else's.
What validation does and doesn't tell you
A validator confirms the number is internally consistent. It can't tell you whether the account is open, who owns it, or whether they're trustworthy. If payment details change unexpectedly, always confirm through a channel other than the message that brought the change. If something feels off, talk to your bank before sending money.