How long is a Portuguese IBAN?

Exactly 25 characters. The structure is PT, two check digits, a 4-digit bank code, a 4-digit branch code, an 11-digit account number, and 2 national NIB check digits. Anything else is invalid.

What is the NIB in a Portuguese IBAN?

The NIB (Numero de Identificacao Bancaria) is the 21-digit Portuguese domestic account number. The IBAN is PT plus two check digits plus the full NIB, and the last two NIB digits are themselves a national check.

How does the MOD-97 check work?

The first four characters are moved to the end, each letter is replaced by a number (A=10 to Z=35), and the result is divided by 97. The remainder must equal 1 for the IBAN to be structurally valid.

Does a valid result mean the account exists?

No. MOD-97 catches typos and transposed digits but cannot confirm the account is real or open. Only the bank can confirm that.

Is my IBAN sent anywhere?

No. All validation runs locally in JavaScript. Nothing is uploaded, logged, or stored, and the tool works offline once loaded.

Portugal IBAN Validator

Portuguese IBANs are 25 characters long and wrap the domestic NIB (Numero de Identificacao Bancaria) inside the standard IBAN frame. Because the NIB has its own bank, branch, account, and two-digit national check, it is one of the most structured IBANs in Europe. This validator breaks it apart and checks it instantly, entirely in your browser.

How it works

A Portuguese IBAN always begins with PT, followed by two check digits, a four-digit bank code, a four-digit branch code, an eleven-digit account number, and two national NIB check digits:

PT  kk  bbbb  ssss  aaaaaaaaaaa  dd
^   ^   ^     ^     ^            NIB check digits (2)
|   |   |     |     account number (11 digits)
|   |   |     branch code (4 digits)
|   |   bank code (4 digits)
|   check digits (2)
country code

The validator runs three checks: the length must be exactly 25; the 21-digit BBAN must be all digits; and the ISO 7064 MOD-97-10 checksum must pass. For the checksum the first four characters (PTkk) are moved to the end, every letter is replaced by its numeric code, and the resulting long integer must leave a remainder of 1 when divided by 97. The computation is folded digit-by-digit so no big-integer library is needed.

Worked example

Take PT50 0002 0123 1234 5678 9015 4: country code PT, check digits 50, bank 0002, branch 0123, account 12345678901, NIB check 54. Rearranging the IBAN and dividing by 97 leaves remainder 1, so the checksum passes.

Tips

Almost every Portuguese IBAN you will see starts with PT50, because 50 is the most common IBAN check value for the NIB scheme. Keep all leading zeros in the bank and branch codes, since dropping one shortens the IBAN and fails the length check. All figures are processed locally and never uploaded.