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AWB Number Format and the Mod-7 Check Digit Explained
Every airline air waybill number follows the same 11-digit structure, and the last digit is not random. It is a check digit, calculated with a simple modulo 7 rule, that lets anyone confirm a number is at least plausible before sending it to an airline system. This guide explains the format, works through the arithmetic step by step, and is precise about which typing errors the check catches and which it misses.
Key takeaways
- An AWB number is a 3-digit airline prefix plus an 8-digit serial; the 8th serial digit is the check digit.
- The check digit is the first seven serial digits, read as one number, divided by 7: the remainder is the check digit. The prefix is not used.
- Because a remainder of 7 is impossible, a valid check digit is always 0 to 6. A final digit of 7, 8 or 9 means the number is wrong.
- The check catches most single-digit typos and most swapped digits, but not all of them.
- House waybill numbers issued by forwarders do not follow this scheme at all.
The format: prefix + serial
A master air waybill number such as 020-12345675 has two parts:
- Prefix (020): a 3-digit code identifying the issuing airline, assigned through IATA and also used in airline accounting. It tells you which carrier's system holds the tracking data. Examples include 020 for Lufthansa Cargo, 115 for Air Serbia, 157 for Qatar Airways Cargo, 235 for Turkish Cargo and 724 for Swiss WorldCargo. Our airline prefix list covers the rest.
- Serial (12345675): eight digits. The first seven (1234567) are the running number. The eighth (5) is the check digit.
Airlines issue serials in blocks, often to forwarders who hold stock of numbers and assign them as they book shipments. The check digit is what makes a random-looking number self-validating.
How the check digit is calculated
The rule is short:
- Take the first seven digits of the serial and treat them as a single whole number.
- Divide by 7.
- The remainder (0 to 6) is the check digit.
The prefix plays no part. Two different airlines can issue the same serial, and the check digit will be identical for both.
Worked example 1: Lufthansa Cargo, 020
Suppose a booking confirmation shows 020-1234567? and the last digit is illegible.
- Seven-digit serial: 1,234,567
- 7 × 176,366 = 1,234,562
- 1,234,567 − 1,234,562 = 5
The check digit is 5, so the full number is 020-12345675.
Worked example 2: Air Serbia, 115
Check whether 115-74489030 is valid.
- Seven-digit serial: 7,448,903
- 7 × 1,064,129 = 7,448,903
- Remainder: 0
The last digit is 0, which matches. The number passes.
Worked example 3: Turkish Cargo, 235
Check 235-94456121.
- Seven-digit serial: 9,445,612
- 7 × 1,349,373 = 9,445,611
- 9,445,612 − 9,445,611 = 1
The last digit is 1. Valid.
If you do this on a phone calculator, divide by 7, take the whole-number part, multiply it back by 7 and subtract from the original. In a spreadsheet, =MOD(7448903,7) does it in one step.
What the check digit catches, and what it misses
A check digit is only useful if you know its limits. The mod 7 scheme is simple, and its blind spots follow directly from the arithmetic.
Single-digit substitutions
If you mistype one of the first seven digits, the serial changes by the difference between the two digits multiplied by a power of ten (1, 10, 100 and so on). No power of ten is divisible by 7, so the error goes unnoticed only when the difference itself is a multiple of 7. Between two digits 0 to 9, that means a difference of exactly 7. So the check misses these substitutions and catches every other one:
- 0 typed as 7, or 7 typed as 0
- 1 typed as 8, or 8 typed as 1
- 2 typed as 9, or 9 typed as 2
A real illustration: 115-74489030 is valid, and so is 115-04489030, because 7,000,000 is divisible by 7. If someone reads the leading 7 as a 0, the check digit will not save you.
By contrast, change the sixth serial digit of 235-94456121 from 1 to 7 and you get serial 9,445,672, which leaves a remainder of 5. The written check digit is 1, so the error is caught.
A mistake in the check digit itself is always caught, because each serial has exactly one correct check digit. A final digit of 7, 8 or 9 is impossible.
Transposed digits
Swapping two adjacent digits a and b changes the serial by 9 × (a − b) × a power of ten. Since neither 9 nor any power of ten is divisible by 7, the swap is missed only when a and b differ by 7: the pairs 0/7, 1/8 and 2/9. For example, typing 020-12346575 instead of 020-12345675 is caught, because 1,234,657 leaves a remainder of 4, not 5.
There is one more gap worth knowing. Because 1,000,000 leaves a remainder of 1 when divided by 7, swapping the first and seventh serial digits never changes the remainder, whatever those digits are. Other non-adjacent swaps within the first seven digits behave like adjacent ones: they are missed only for the 0/7, 1/8 and 2/9 pairs. A swap between the seventh serial digit and the check digit is caught whenever the two digits differ.
A passing check digit means the number is well formed, not that it exists. A valid-looking number can still belong to a different shipment, a different airline (wrong prefix), or a booking that has not yet been created in the airline's system.
Common formatting variants
The same number turns up in many shapes on documents, emails and portals:
| As written | Notes |
|---|---|
| 020-12345675 | Standard form with hyphen after the prefix |
| 020 1234 5675 | Grouped with spaces, common on printed labels |
| 02012345675 | No separators, typical in system exports |
| 2012345675 | Leading zero lost; only 10 digits |
| LH 020-12345675 | Carrier code added in front; strip it before checking |
The leading-zero problem deserves a special mention. Spreadsheet programs such as Excel treat 02012345675 as a number and silently drop the leading zero, so prefix 020 becomes 20 and the AWB becomes 10 digits long. Any lookup then fails or hits the wrong carrier. To avoid it, format the column as Text before pasting, or rebuild the number with =TEXT(A2,"00000000000"), which pads it back to 11 digits. Many airline prefixes begin with zero, so this is a routine problem in shipment spreadsheets, not an edge case.
House waybills do not follow this scheme
A house air waybill (HAWB) is issued by a freight forwarder, not by an airline. Its number is whatever the forwarder's system generates: it might be all digits, it might include letters or a branch code, and it might be any length. The mod 7 check does not apply, and running it on a HAWB tells you nothing. If the number on your paperwork does not fit the 3 + 8 pattern, it is probably a house number, and you will need the master AWB from your forwarder to track the flight. Master AWB vs House AWB explains the difference.
What to do if the check digit fails
- Recount the digits. You need exactly 11. Ten usually means a lost leading zero; twelve often means a stray digit from a reference number.
- Look for look-alike characters. O for 0, I or l for 1, S for 5 and B for 8 are frequent in numbers copied from scans or handwriting.
- Compare against the original document. Go back to the AWB, the booking confirmation or the forwarder's pre-alert rather than a forwarded email.
- Confirm it is a master number. If it came from a forwarder invoice, it may be a house number.
- Ask the issuing agent. If nothing fixes it, the forwarder or agent who issued the waybill can confirm the correct number from their system.
If a number passes the check but still returns nothing, see our troubleshooting page: typical causes include a booking not yet transmitted to the airline or a shipment handled by a different carrier than the prefix suggests.
Checking and tracking numbers on AWBTracking.net
Our free AWB validator runs the mod 7 check on any number you paste in, so you can catch a typo before you start chasing a shipment that does not exist. When the number passes, paste it into the lookup to see the latest events from the issuing airline.