The check digit
Multiply the first six digits by 7, 6, 5, 4, 3 and 2, add them up, and the units digit of that sum is the seventh digit. One transposed or mistyped digit fails it — which is the whole point of the check.
Tools · Maritime
IMO number validator
Check an IMO number's check digit — the single mistake that quietly invalidates a Notice of Readiness or a certificate reference — and see exactly how the digit is derived. Or paste a whole list and validate it at once.
Computed in your browser.
Nothing is uploaded. With usage logging on, only the count of numbers checked is kept — never the
numbers; switch it off in the account bar.
How it works
Seven digits, one of them a checksum.
Where it bites
A wrong IMO number on a Notice of Readiness or a certificate reference is exactly the kind of quiet error that surfaces later in a dispute. Validating it takes a second and removes the excuse.
The same check runs inside the Notice of Readiness generator as you type.