CII and EEXI Explained: What Every Officer Needs to Know in 2026

The Energy Efficiency Existing Ship Index is a technical measure, calculated once, verifying that a ship's design — engine power, hull form, and any energy-saving devices fitted — meets a required efficiency threshold based on ship type and size. It is closer in spirit to a design certificate than an operational one: pass it, and no ongoing annual recalculation is required unless the ship is significantly modified.

A ship that does not meet its required EEXI threshold has real options short of a rebuild — engine power limitation is the most common, technically a software and verified limit on maximum continuous rating rather than a hardware change, and it is now a routine fitment across a large share of the existing world fleet.

The Carbon Intensity Indicator is entirely different in character. It is calculated every single year, using the ship's actual fuel consumption and distance sailed over that specific year — not its design, its actual operation. The same ship, run efficiently one year and inefficiently the next through decisions entirely outside the original design, can move between rating letters year to year.

This is the detail that makes CII, unlike EEXI, something crew genuinely influence in real time: voyage speed, routing, hull and propeller condition, and auxiliary load management all feed directly into the year's actual CII figure, in a way that no crew decision can meaningfully change an EEXI result once the ship is built.

CII is calculated as CO2 emitted per capacity-tonne-mile, expressed as an Attained CII figure, then compared against a Required CII reference line that tightens progressively year over year through 2030. The result is converted into a letter rating — A, B, C, D or E — using ship-type-specific boundaries published by IMO, with A representing the most carbon-efficient performance for that ship type and size, E the least.

The reference line becoming stricter each year is the detail most often missed: a ship achieving exactly the same operational efficiency in 2027 as it did in 2024 will still see its rating letter decline over that period, purely because the bar it's measured against keeps moving. Standing still is a slow fail under CII, by design.

A ship rated D for three consecutive years, or E for even a single year, is required to submit a corrective action plan as part of its Ship Energy Efficiency Management Plan, setting out how it intends to reach at least a C rating. This is a genuine administrative and operational burden, but it is not, by itself, a trading restriction — a D or E-rated ship can still trade.

The practical consequence that actually bites is commercial rather than regulatory: charterers increasingly screen fleets by CII rating before fixing, and a poor rating on a specific ship can mean it is quietly passed over in favour of a better-rated sister vessel, well before any regulatory consequence is ever triggered.

Because CII is calculated from actual annual fuel consumption and distance, the operational choices that most directly affect it are the ones officers already influence every voyage: maintaining an efficient service speed rather than sailing fast and waiting at anchor, keeping the hull and propeller in good condition between dry dockings, and managing auxiliary and boiler load rather than running equipment continuously out of habit.

None of these are new practices invented for CII — they are the same efficient-operation habits good engineers and masters have always valued. What has changed is that they now show up in an annual number the whole company, and increasingly the charterer, can see.

The single most consequential misunderstanding is treating EEXI compliance as though it settles CII too. It does not. A ship can pass EEXI comfortably on the strength of its design and still earn a D or E CII rating through inefficient operation in a given year — and conversely, an older ship with a mediocre EEXI margin can still achieve a strong CII rating through disciplined operation. They are independent measures, and passing one provides no guarantee about the other.

Understanding the two thresholds in principle is one thing; checking a specific ship's actual attained figure against its required line, for the current year, is the calculation that matters day to day. The free CII Calculator in ShipCrewFinder's Crew Toolkit runs exactly that check — enter the ship's particulars and annual consumption figures and see the attained CII, the required reference line, and the resulting rating letter.