A Croatian IBAN is always 21 characters long. Here is what each part of it means, with a real example broken down field by field — and a checker that runs on your machine.
Croatia gives an unusually generous seven digits to the bank code — more than any other short IBAN in the region — and ten to the account. Croatia joined the euro in 2023, but the IBAN structure itself did not change.
The two digits straight after HR are not part of the account — they are a checksum over everything else. Move the first four characters to the end, turn every letter into a number (A=10 … Z=35), divide the result by 97, and a genuine IBAN always leaves a remainder of exactly 1. That is what the box above is doing, on your machine, with nothing sent anywhere.
If the number is on a scanned PDF you cannot select, retyping 21 characters is where mistakes get made. Snip2Field sits on your Windows desktop: press a hotkey, drag a box over the IBAN, and it reads the field, runs this exact checksum and copies it — ready to paste into your books or a transfer form. Fully offline.
See Snip2FieldExactly 21, always. That is HR, two check digits, and 17 characters of account detail. Anything longer or shorter is not a valid HR IBAN, whatever else is right about it.
It is the 7 characters directly after the check digits. In the example HR12 1001 0051 8630 0016 0, that is 1001005.
You can tell whether it was written down correctly: the check digits catch a single wrong character or two swapped ones. You cannot tell whether the account exists — only the receiving bank knows that, which is what the recipient-name check does when a transfer is made.