How this works
A Portuguese IBAN is just the NIB with a prefix. To build it, append '252900' to the NIB (which encodes 'PT00'), take the remainder of dividing that huge number by 97, and the check digits are 98 minus that remainder. Going the other way, strip 'PT' and the two leading digits and you have the 21-digit NIB — but first we confirm the IBAN passes the mod-97 check (the remainder must be exactly 1).
- 1
Pick the direction
NIB → IBAN to get the IBAN from a 21-digit NIB, or IBAN → NIB for the reverse.
- 2
Paste the number
Spaces and the "PT" prefix are ignored. The conversion happens as you type.
- 3
Check the blocks
Read the resulting IBAN/NIB and the split into bank, branch and account. Copy with one click.
Frequently asked
What is the difference between NIB and IBAN?
NIB is the old 21-digit format, used only in Portugal. IBAN is the international format: it takes the NIB, prepends "PT" and two check digits, giving 25 characters. In Portugal the IBAN is literally "PT" + check digits + the whole NIB. Since 2014 transfers use IBAN, but many older documents still carry the NIB.
Why does a Portuguese IBAN almost always start with "PT50"?
The two digits after "PT" are computed by a formula (mod 97) from the NIB. Because the Portuguese NIB already contains its own check digits, that formula nearly always yields "50". If your IBAN does not start with PT50, the most likely cause is a mistyped digit in the NIB.
Does this tool validate the IBAN?
Yes. When converting IBAN to NIB it checks that the length is 25, that it starts with "PT" and that it passes the mod-97 check (the remainder must be 1). If anything fails it warns you instead of returning garbage. Everything runs in your browser — the number never leaves your computer.
What do the NIB blocks mean?
The 21 digits split into four parts: the first 4 identify the bank, the next 4 the branch, the following 11 are the account number, and the last 2 are local check digits. The tool shows this split so you can check each block.
Does it confirm the account exists or who owns it?
No. The conversion and validation are purely mathematical. A number can pass the formula and still match no real account, or belong to someone else. Before sending money, always confirm the IBAN with the recipient.
DISCLAIMER
This tool only performs the mathematical conversion and format validation. It does not confirm whether the account exists, is active or who it belongs to, and queries no bank. Before making a transfer, always confirm the IBAN directly with the recipient. Not financial advice.