Read the parts without guessing the bank
Every IBAN starts with a country code and two numerical check digits. The remaining characters follow the national basic bank account number structure. That national portion can include bank, branch and account identifiers, but the exact positions and total length differ by country.
Do not infer a recipient's residence from the country code or assume that every bank account worldwide has an IBAN. The identifier belongs to the account format used by participating jurisdictions, not to every possible international payment route.
How the mod-97 checksum is tested
The calculation is useful because it can be performed locally without asking a bank about the account.
Normalize the input
Remove spaces and use uppercase letters so presentation formatting does not change the value.
Move the first four characters
Place the country code and check digits at the end of the string.
Translate letters
Convert A through Z to the numbers 10 through 35.
Calculate the remainder
A correctly formed IBAN produces a remainder of 1 when the resulting number is evaluated modulo 97.
What each check can and cannot establish
| Check | Can establish | Cannot establish |
|---|---|---|
| Character and length check | The value follows an expected basic shape | The account exists or is open |
| Checksum | Characters are mathematically consistent | The account holder's identity |
| Country format | Length and national structure match published rules | The account accepts the payment currency |
| Payee-name service | A system-specific name comparison where offered | The honesty of the person requesting payment |
Use every available verification layer. No format check can replace independent recipient confirmation.
A valid IBAN can still be fraudulent
An attacker changes an invoice and inserts an IBAN that belongs to an account the attacker controls. The checksum passes because the account number is structurally valid. A format checker correctly reports validity, yet the payment instruction is still fraudulent.
The defense is procedural: call the supplier on a previously verified number, read back the changed details and document who confirmed them. Mathematical validity and business authorization answer different questions.
A checksum answers a narrow question about structure
An IBAN combines a country code, check digits and a country-specific basic bank account number. The international structure supports automated processing, while the national section follows rules set for that country. Display spaces can be removed for calculation, but the underlying letters and digits must remain in the same order.
The mod-97 check is designed to catch many transcription and formatting errors. Passing it means the characters are mathematically consistent with the checksum. It does not contact a bank, show that an account is open, confirm the account currency or prove who controls it. A fabricated or misdirected IBAN can still be structurally valid.
Use validation before payment as one layer. Obtain the IBAN from a trusted source, compare the beneficiary name where a bank offers a name-checking service and confirm changed instructions through a known channel. If a value fails, return to the original source rather than guessing a digit. If it passes, continue with identity, purpose and route checks instead of treating the green result as authorization.
Use the identifier safely
Before paying, run the value through the IBAN format checker and then verify the recipient separately.
If the bank also asks for a BIC, read how BIC and SWIFT codes work.
Run the checksum locally
Use the checker to catch structural errors, then complete a separate identity and account-owner check.
IBAN Format Checker
Check the length, characters and ISO 13616 mod-97 checksum locally in your browser.
IBAN standard and payment references
ISO 13616 defines the IBAN structure, while payment guidance explains its operational use. A valid checksum does not confirm the owner or authorize a payment.
Questions about what an IBAN proves
Is an IBAN secret?
It is routinely shared to receive payments, but it is still financial information that should be handled carefully and shared only for a legitimate purpose.
Why are spaces shown in an IBAN?
Spaces make the identifier easier for people to read. Electronic processing generally uses the continuous character string.
Can FROM.you confirm the bank account?
No. The local checker evaluates structure and checksum only and does not query a bank or registry.
This page uses worked reasoning and authoritative references; it does not claim first-hand testing or personalized advice. See our editorial policy.
Continue through the international banking collection for account access, currency holding, payment rails and protection questions.