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IMO number validator

IMO numbers are unique 7-digit identifiers assigned by IHS Maritime (on behalf of the IMO) to ships of 100 GT and above engaged in international voyages, and to all motorised inshore craft of 12 m and above. The number is permanent — it stays with the vessel regardless of flag, name, or owner change.

How the checksum works

An IMO number is six significant digits followed by one check digit. To validate: multiply each of the first six digits by the weights 7, 6, 5, 4, 3, 2 respectively; sum the products; the units digit of the sum (i.e. sum modulo 10) must equal the check digit. This makes it easy to detect single-digit transcription errors.

Example: IMO 9074729 — digits 9,0,7,4,7,2 × 7,6,5,4,3,2 = 63+0+35+16+21+4 = 139 → last digit = 9. ✓

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When to use this tool

Cross-checking IMO numbers on a B/L or manifest against the ship's data + AIS + CSR. Verifying that a "dark fleet" or sanctions-linked vessel candidate's cited IMO is real (fake IMOs are a common evasion tactic). Confirming a P&I certificate + Blue Card is legitimately associated with the specific vessel by IMO.

Worked example

Scenario: A B/L presented for cargo release names the carrying vessel as IMO 9370211.

Check: 9,3,7,0,2,1 × 7,6,5,4,3,2 = 63+18+35+0+6+2 = 124 → last digit = 4. Actual last digit is 1 → INVALID checksum.

Interpretation: B/L IMO likely a transcription error or fraud. Cross-check against carrier + shipper before acting. Real IMO for that vessel may differ by a single digit.

Regulatory basis

IMO Res. A.600(15) (1987) — IMO Ship Identification Number Scheme. Assigned by IHS Maritime on behalf of the IMO. Mandatory for all SOLAS-flagged commercial vessels 100 GT + since 1996. Recorded on the Continuous Synopsis Record (CSR) under SOLAS XI-1/5. Permanent identifier — survives name + flag + owner changes. Complements the IMO Company Number for the shipowner + manager entities.

See also