Watchkeeping
IMO and MMSI number check
Check an IMO number's check digit, or see what an MMSI says about itself: the kind of station and its country.
Fill in the fields to see the result.
How it works
An IMO number has seven digits; the last is a check digit. Multiply the first six by 7, 6, 5, 4, 3 and 2, add them up: the last digit of the sum must equal the seventh. Example: IMO 9074729: 9×7 + 0×6 + 7×5 + 4×4 + 7×3 + 2×2 = 139, ends in 9. A valid check digit doesn't mean the number is in use.
An MMSI has nine digits. A ship's starts with its three maritime identification digits (MID, the flag country); 00 + MID is a coast station, 0 + MID a group, 111 + MID a SAR aircraft, 99 + MID an AIS aid to navigation, 8 + MID a handheld VHF; 970 is an AIS-SART, 972 a man-overboard device, 974 an EPIRB with AIS. MIDs follow ITU-R M.585; the ITU MARS database is the authority.
For training and cross-checking. Not a substitute for approved navigation equipment, nautical publications and the ship’s own procedures. Calculations run in your browser and nothing you type is stored; a PDF you download is made on our server and not kept.
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