What is a Greek IBAN and how long is it?

A Greek IBAN (Διεθνής Τραπεζικός Αριθμός Λογαριασμού) is always exactly 27 characters long. It begins with the two-letter country code GR, followed by two IBAN check digits computed via the ISO 7064 MOD-97-10 algorithm, and then a 23-digit BBAN (Basic Bank Account Number) made up of a 3-digit bank code, a 4-digit branch code and a 16-digit account number — all purely numeric.

What is the MOD-97 checksum and why does it matter?

The ISO 7064 MOD-97-10 algorithm rearranges the IBAN by moving its first four characters to the end, expands each letter to its two-digit numeric equivalent (A = 10, B = 11 ... Z = 35), then folds the entire string through progressive modulo-97 arithmetic. If the final remainder equals exactly 1 the structure is intact. Any single transposition or mis-typed digit almost always changes the remainder, so the vast majority of keying errors are caught before a payment is sent.

What do the bank code and branch code in a Greek IBAN mean?

In the Greek BBAN layout the first three digits identify the bank (assigned by the Bank of Greece and the DIAS interbank clearing network), while the following four digits identify the specific branch. Together they pinpoint where the account is held. The remaining 16 digits are the individual account number assigned by the bank.

Which Greek banks use the GR IBAN prefix?

All banks licensed to operate in Greece and offering euro-denominated accounts issue IBANs starting with GR. This includes Alpha Bank (bank code 011), National Bank of Greece (011), Piraeus Bank (017), Eurobank (026), Attica Bank (015), and branches of international banks operating in Greece. The 3-digit bank code in the BBAN identifies the specific institution.

Can this tool confirm that the account actually exists?

No. A "valid" result means the IBAN is structurally correct — it starts with GR, is exactly 27 characters, the BBAN is all numeric, and the MOD-97 checksum passes. It cannot confirm that an account with this number is currently open or belongs to a particular person. Only your bank or the recipient bank can verify that. Always confirm account details directly with the account holder before sending money.

Is my banking data safe when I use this tool?

Completely. The entire validation runs inside your browser using JavaScript. No IBAN, no account number and no personal data of any kind is ever sent to a server. You can even use this tool offline once the page has loaded.

Greek IBAN Validator

A Greek IBAN validator that checks every structural layer of the number in real time — the ISO 7064 MOD-97-10 checksum, the 3-digit bank code, the 4-digit branch code and the 16-digit account number format. It is built for anyone who needs to verify a Greek IBAN before making a SEPA bank transfer, integrating it into a payment form, or confirming account details shared by a counterparty.

How it works

Greece adopted the IBAN standard (ISO 13616) for all domestic and international euro transfers through the DIAS interbank clearing network. Every Greek IBAN is exactly 27 characters and follows a fixed, entirely numeric BBAN layout:

Position	Length	Field	Content
1-2	2	Country code	Always `GR`
3-4	2	IBAN check digits	Computed by MOD-97
5-7	3	Bank code	Numeric bank identifier
8-11	4	Branch code	Numeric branch identifier
12-27	16	Account number	Numeric account identifier

The validator runs three independent checks.

Check 1 — ISO 7064 MOD-97-10 (overall IBAN checksum). The first four characters (GR plus the two check digits) are moved to the end of the string. Then every letter is expanded to its two-digit numeric equivalent: G becomes 16, R becomes 27. The resulting long digit string is folded through progressive modulo-97 arithmetic — dividing by 97 one digit at a time so no JavaScript integer overflow occurs even for the longest IBANs in the registry. The IBAN is structurally valid if and only if the final remainder equals exactly 1.

Check 2 — Length and country code. Greek IBANs are always 27 characters starting with GR. Any deviation — a miscount when copying, a truncated paste, or an IBAN from another country — is flagged immediately with the actual versus expected character count.

Check 3 — BBAN format. Even after passing MOD-97, the tool inspects the 23-character BBAN individually: it must consist entirely of digits. A BBAN containing any letters would indicate the IBAN was corrupted or belongs to a different country’s format.

Worked example

Take the test IBAN GR16 0110 1250 0000 0001 2300 695. After stripping spaces the input is GR1601101250000000012300695 — exactly 27 characters.

Rearrange and expand: move GR16 to the end to get 01101250000000012300695GR16. Expanding letters: G = 16, R = 27. The numeric string becomes 011012500000000123006951627 16. Folding this through progressive mod-97 gives a remainder of 1 — checksum passes.
BBAN breakdown:
- Bank code = 011 (3 digits, valid)
- Branch code = 0125 (4 digits, valid)
- Account number = 0000000012300695 (16 digits, valid)
Result: all checks pass — the IBAN is structurally valid.

Now change the last digit to 6 (GR1601101250000000012300696). The MOD-97 remainder is no longer 1, so the checksum fails immediately and the tool shows “Invalid — IBAN checksum (MOD-97) failed” in red. This is how IBANs protect against single-digit transcription errors in practice.

Every calculation runs entirely in your browser. No data is sent anywhere.