CII correction factors and voyage adjustments (G5)

Attained CII is a blunt instrument by design: total CO₂ over the year divided by capacity and distance, as the CII guide explains. It cannot tell a ship that burned fuel forcing through ice, or that ran cargo pumps for a day at anchor, from a ship that simply sailed inefficiently. The 2022 Interim guidelines on correction factors and voyage adjustments, G5, exist to make that distinction MEPC.355(78) · G5. They list a closed set of situations in which fuel may be deducted from the calculation or a term of the formula corrected, so that the rating reflects the ship's efficiency rather than its circumstances — with the explicit caveat, in the guideline's own words, that their use should in no way undermine the goal of reducing the carbon intensity of international shipping. This page lists what G5 actually defines, how it changes the attained value, and where the corrected value then lands.

Two kinds of correction

G5 separates two mechanisms MEPC.355(78) · G5. A voyage adjustment deducts the fuel consumed in a defined voyage period, together with the distance travelled in that period, from the calculation of attained CII — subject to the ship meeting the period's qualifying conditions. A correction factor is a factor in the numerator or denominator of the CII formula that adjusts the calculation. The difference matters in practice: an adjustment removes a slice of the year; a factor rescales a term for the whole year.

What G5 defines

Everything below is what the guideline text provides for. It is a closed list, each item with its own conditions; nothing on it is a general discount.

Parameter	Applies to	What it does
FC_voyage, D_x	Any ship, for voyage periods in the situations of MARPOL Annex VI regulation 3.1 that may endanger safe navigation, and for sailing in ice conditions — an ice-classed ship in a sea area within the ice edge	Voyage adjustment: deducts the fuel consumed in the period and the associated distance travelled; periods reported to the Administration in the G5 appendix 2 format
AF_Tanker,STS	Tankers engaged in ship-to-ship voyages as G5 defines them — operating under MARPOL Annex I regulation 41.2 and the OCIMF STS guide, on legs of at most 600 nautical miles and 72 hours	Correction factor on the fuel of STS voyages, including transfer at the offshore location, waiting periods and discharge in port; a DWT-based factor fixed in the guideline
AF_Tanker,Shuttle	Shuttle tankers equipped with dynamic positioning and specialised cargo handling for loading at offshore installations	Correction factor on the ship's total fuel consumption; a DWT-based factor fixed in the guideline; excludes the other deductions
FC_electrical	Fuel used to generate electrical power for refrigerated containers on any ship, cargo cooling or reliquefaction on gas and LNG carriers, and electric discharge pumps on tankers	Deduction of that fuel, calculated per G5 appendix 1 part A; only a share is allowed, and the share falls every year from 2023 on the schedule the guideline fixes
FC_boiler	Oil-fired boiler fuel used for cargo heating and cargo discharge on tankers	Deduction of that fuel per appendix 1 part B; same declining allowed share as FC_electrical
FC_others	Standalone engine-driven cargo pumps during discharge operations on tankers	Deduction of that fuel; same declining allowed share
f_i, f_m, f_c, f_iVSE	Ice-classed ships (capacity factor and the IA Super / IA factor), chemical tankers (cubic capacity), ships with voluntary structural enhancement — the EEDI/EEXI correction factors	Applied in the denominator with capacity, only where they are included in the ship's EEDI or EEXI Technical File

Reference facts, cited — not engine coefficients. MEPC.355(78) · G5

The guideline also fixes what may not be combined MEPC.355(78) · G5: where a tanker applies the STS or shuttle factor, the electrical, boiler and other-consumption deductions are not used, and none of those three deductions applies to periods covered by a voyage adjustment. Whatever is applied, the ship still reports its total fuel consumption by fuel type, total hours under way and total distance to the Administration under regulation 27 of MARPOL Annex VI MEPC.328(76) · Reg. 27, records the relevant data in the logbook, and reports each parameter it used.

How it changes the attained value

G5 rewrites the attained CII formula of the G1 guidelines rather than adding a step after it MEPC.352(78) · G1 MEPC.355(78) · G5. In the numerator, each fuel's annual consumption is reduced by the voyage-adjustment fuel, the STS or shuttle removal and the allowed share of the electrical, boiler and other deductions before the CO₂ conversion factor is applied. In the denominator, the EEDI and EEXI correction factors multiply the capacity, and the voyage-adjustment distance is subtracted from the total distance. The result is the corrected attained annual operational CII, and G5 is explicit that the A–E rating under the G4 guidelines is carried out using that corrected value.

There is no worked example on this page. Carbonlogy's CII engine computes attained CII from a ship's reported totals and rates it; it does not model G5 adjustments, so a build-verified example here would be a fabrication rather than a check on anything the product does. The mechanism above is the guideline's, cited; the figures a ship reports under it are its own.

Last reviewed 28 August 2026 · Carbonlogy Compliance Team

How Carbonlogy applies it

Carbonlogy computes each ship's attained CII from its reported CO₂, capacity and distance and rates it against the same reference lines, reduction factors and boundaries as the CII guide. It does not apply G5 voyage adjustments or correction factors: the figure the platform shows is the uncorrected attained value, which for a ship that claims no adjustment is the rated value, and for a ship that does is the starting point from which its verifier-checked deductions are taken. The distinction is kept visible so that no one reads a platform rating as a corrected one, or the other way round.