A Luxembourgish IBAN is always 20 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.
Luxembourg gives three digits to the bank and thirteen characters to the account. Because so many funds and payment institutions are domiciled there, LU IBANs appear on invoices from companies with no other connection to the country.
The two digits straight after LU 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 20 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 20, always. That is LU, two check digits, and 16 characters of account detail. Anything longer or shorter is not a valid LU IBAN, whatever else is right about it.
It is the 3 characters directly after the check digits. In the example LU28 0019 4006 4475 0000, that is 001.
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.