IATA Air Waybill Check Digit (MOD-7) Explained
An air waybill number is a three-digit airline prefix, a seven-digit serial, and a check digit computed by weighting the serial digits 8 to 2 and taking the remainder modulo 7.
Updated 2026-10-01 · 4 min read
What an air waybill number is
An IATA air waybill number has three parts: the three-digit airline accounting prefix, a seven-digit serial number, and a single check digit.
The prefix identifies the issuing carrier and is assigned by IATA. The serial is the shipment reference within that carrier.
The check digit
The seven serial digits are weighted from 8 down to 2 — the first digit by 8, the second by 7, and so on. The weighted products are summed and taken modulo 7; the remainder is the check digit.
For the serial 1234567 the weighted sum is 112, and 112 modulo 7 is 0, so the check digit is 0.
The e-ticket uses the same shape
A 13-digit IATA electronic ticket number is a three-digit airline prefix plus a ten-digit ticket number, whose final digit is a MOD-7 check digit over the preceding digits.
What it does not prove
A valid check digit means the number is well formed. It does not confirm that the shipment exists, that the prefix is still allocated, or that the goods are cleared.
Try it on real data
Frequently Asked Questions
Eleven: a three-digit airline prefix, a seven-digit serial, and one check digit.
Modulo 7, applied to a weighted sum of the seven serial digits weighted 8, 7, 6, 5, 4, 3, 2.
The shape differs (13 digits) but the mechanism is the same MOD-7 check digit over the preceding digits.