What is the format of a Luxembourg IBAN?

A Luxembourg IBAN is always exactly 20 characters long. It begins with the country code LU, followed by 2 check digits, a 3-digit bank identifier, and a 13-character alphanumeric account number. An example in grouped form is LU28 0019 4006 4475 0000.

How does the ISO 7064 MOD-97-10 checksum work?

The check digits are computed by moving the first 4 characters (LUkk) to the end of the string, expanding each letter to its two-digit value (A=10 through Z=35), treating the whole thing as one large integer, and computing the remainder when divided by 97. The IBAN is valid only when that remainder equals exactly 1. Because the number can be hundreds of digits long, this tool folds the modulo progressively character by character so no overflow can occur.

What does the 3-digit bank identifier mean?

In a Luxembourg IBAN, characters 5 to 7 (after LU and the 2 check digits) identify the bank. For example, 001 belongs to BGL BNP Paribas, 002 to Banque et Caisse d'Epargne de l'Etat (BCEE/Spuerkeess), and 019 to ING Luxembourg. This field must be numeric — if letters appear there, the IBAN is structurally malformed.

Can this tool tell me if the account actually exists?

No. This validator checks structure and checksum only. A structurally valid IBAN could still belong to a closed account or contain a transcription error in the account-number field that the checksum does not catch. Only the recipient bank or a real-time verification API can confirm account existence. This tool is for format checking before you submit a payment.

Why does Luxembourg use a 20-character IBAN when some countries use more?

Each country's IBAN length is set by the SWIFT IBAN Registry based on that country's domestic account numbering system. Luxembourg's BBAN (Basic Bank Account Number) consists of a 3-digit bank code and a 13-character account reference, giving 16 BBAN characters plus the 4-character LUkk prefix for a total of 20. Countries with longer domestic account formats (such as Malta at 31 or Saint Lucia at 32) have correspondingly longer IBANs.

Is my data safe when I use this tool?

Completely. The entire validation — length check, BBAN structure check, and MOD-97-10 computation — runs inside your browser using JavaScript. No IBAN, account number, or bank identifier is ever transmitted to a server, stored in a database, or logged anywhere.

Luxembourg IBAN Validator

A Luxembourg IBAN validator that checks every structural rule in one step: the mandatory 20-character total length, the 3-digit numeric bank identifier, the 13-character alphanumeric account field, and the ISO 7064 MOD-97-10 checksum that must equal exactly 1. Results appear as you type, and a Copy button delivers the IBAN in the standard spaced format ready to paste into a payment form or wire instruction.

How it works

Luxembourg IBANs follow the ISO 13616 standard published by SWIFT. The full 20-character string breaks down into four parts:

Part	Position	Length	Format
Country code	1–2	2	`LU` (always)
Check digits	3–4	2	`00`–`99`
Bank identifier	5–7	3	Numeric only
Account number	8–20	13	Alphanumeric

Checksum algorithm (ISO 7064 MOD-97-10):

Strip whitespace and convert to uppercase.
Move the first four characters (LUkk) to the end of the string.
Replace every letter with its two-digit numeric equivalent: A becomes 10, B becomes 11, and so on up to Z becoming 35.
Treat the resulting digit string as a single large integer and compute its remainder when divided by 97, folding progressively to avoid overflow.
The IBAN is valid if and only if the remainder is exactly 1.

The tool also separately validates the BBAN fields: the bank identifier must be exactly 3 numeric digits, and the account field must be exactly 13 alphanumeric characters. Any structural mismatch is reported with a specific error message so you know exactly where to look.

Worked example

Take the well-known Luxembourg test IBAN LU28 0019 4006 4475 0000:

Country code: LU
Check digits: 28
Bank identifier: 001 (BGL BNP Paribas)
Account number: 9400644750000

Rearrangement step: move LU28 to the end:

9400644750000LU28

Letter expansion: L becomes 21, U becomes 30:

940064475000021 30 28

Concatenated digit string: 9400644750000213028

MOD-97 check: 9400644750000213028 mod 97 = 1 — the IBAN is valid.

The formatted output is LU28 0019 4006 4475 0000, grouped in blocks of 4 for readability (the final group has just 4 characters because 20 divides evenly into five groups of 4).

Every calculation runs locally in your browser — no number is ever sent to a server or stored anywhere.