CII compliance in shipping: ratings, standards and software

TL;DR: CII grades every large ship A to E each year on the CO₂ it emits per unit of transport work. Compliance is mandatory under MARPOL Annex VI, the required standard tightens annually, and a single E or three consecutive Ds triggers a corrective action plan. The sharper consequences are commercial: charterers, financiers and cargo owners all read the rating. Software keeps it managed all year rather than discovered at year-end.

Every large ship in the world now gets a yearly grade for how cleanly it moves cargo A to E, like a school report. That grade is the CII, and it has quietly become one of the most commercially important numbers in shipping.

A good rating opens doors with charterers. A poor one invites scrutiny, corrective plans and awkward questions from the people paying for the voyage.

This guide is the practical companion for managing CII compliance: the rating scale, who it applies to, the standards behind it, what a poor grade triggers, and how software keeps fleets on the right side of the line.

How CII works

CII stands for Carbon Intensity Indicator the IMO's annual measure of a ship's operational carbon efficiency. Each year a vessel's attained CII is calculated from its fuel, distance and capacity, then compared against a required value for its ship type and size; the gap between the two sets the grade. The full formula and a worked example are in How is CII calculated?, and for the plain-English definition what CII means and its full form see What is CII in shipping?

Which ships does CII apply to?

CII applies to cargo, RoPax and cruise ships of 5,000 GT and above engaged in international trade regardless of flag, owner or where the company is based. That threshold captures the vessels responsible for around 85% of shipping's CO₂ emissions: bulk carriers, tankers, container ships, gas carriers, general cargo ships and the large passenger segment. If a ship is above the line, there is no opt-out the rating is calculated, verified and recorded every year it trades.

CII vs EEXI: what's the difference?

CII is easily confused with EEXI, but they measure different things: EEXI is a one-time check of a ship's technical design efficiency (the ship on paper), while CII grades how efficiently the ship is actually operated each year (the ship in service). A vessel can pass EEXI comfortably and still rate D on CII if it is run inefficiently.

The CII rating scale: A to E explained

The grades are set against the required CII for the year, with the bands drawn statistically around that line so the grade reflects how far off the pace a vessel is, not just whether it passed.

• A — major superior. Comfortably beating the requirement; a genuine selling point in fixtures.
• B — minor superior. Ahead of the requirement, with headroom to spare.
• C — moderate. Broadly on target; the minimum grade regulators consider acceptable.
• D — minor inferior. Below the requirement; three consecutive Ds trigger a corrective action plan.
• E — inferior. Well below the requirement; a single E triggers the corrective plan immediately.

The rating is based on the previous calendar year's verified data, which is why it cannot be managed retrospectively. By the time a grade is issued, the year that produced it is already over.

The standards behind CII: a bar that rises every year

CII compliance is mandatory. It entered force in January 2023 under the IMO's MARPOL Annex VI, and here is the part operators most often underestimate: the required CII is not a fixed target. The IMO tightens the requirement every year through reduction factors the bar started at 5% below the 2019 baseline in 2023 and reaches 11% by 2026; from 2027 it tightens by 2.625% each year, hitting 21.5% below baseline by 2030.

Here is what that looks like in practice. Take a bulk carrier that earns a C this year. Change nothing same speed, same routes, same hull and next year it rates D, because the required CII tightened while the ship stood still. That one drop can be enough for a charterer screening on CII to fix a rival vessel instead. The grade didn't slip because the ship got worse; it slipped because the bar moved. That is why CII has to be managed forward, not reviewed at year-end.

What happens if a ship rates D or E?

A single E rating, or a D three years in a row, triggers a formal consequence: the ship must produce a corrective action plan showing how it will return to C or better, approved as part of its energy-efficiency management plan. There is no direct IMO fine the real costs are commercial. Charterers screen on ratings, some charter parties now carry CII clauses, and a poorly rated ship becomes harder to fix at good rates.

How operators improve their CII rating

Every lever works the same way: emit less CO₂ for the same transport work. In practice, operators reach for four:

• Speed management — modest reductions cut fuel consumption disproportionately; the single biggest lever.
• Routing and weather — smarter routes and weather choices avoid fuel burned fighting conditions.
• Hull and propeller condition — fouling quietly adds double-digit percentages to consumption; cleaning claws it back.
• Cargo and ballast planning — fewer empty legs and better utilisation improve the ratio directly.

How CII compliance software helps

The maths behind CII is simple. Managing it across a fleet, all year, is not and that is the problem CII compliance software exists to solve. It keeps the score live, so operators see attained CII per vessel today rather than when the year's data is compiled. It forecasts the year-end, projecting which ships hold their grade and which drift towards a D by November. And it tests decisions before they are made simulating what a speed change, routing choice or fuel switch does to the rating, and to the EU ETS bill, before the voyage is fixed.

Underneath all three sits data quality. Ratings are only as good as the fuel and distance figures behind them, which is why platforms such as ZeroNorth's Emission Analytics validate every figure at the point of collection so the number a verifier sees is one the operator can stand behind.

Beyond compliance: the commercial angle

It is tempting to file CII under regulation and stop there. The operators getting the most from it treat the rating as a commercial signal instead. A ship's CII trajectory is really a fuel-efficiency trajectory the same levers that protect the rating cut fuel bills and EU ETS exposure at the same time, so voyage optimisation that saves fuel is CII compliance that pays for itself.

There is a market signal too. Charterers and financiers increasingly use CII ratings as shorthand for how well a ship is run, Poseidon Principles banks assess portfolios on carbon intensity, and cargo owners look down the chain at the ships carrying their goods. An A or B is becoming a selling point in fixture negotiations; a D is becoming a discount.

Where to go next

The detail lives in four companion guides. What is CII in shipping? is the plain-English starting point. How is CII calculated? breaks down the formula, the inputs and the rating bands.

Because with a bar that rises every year, the question is never whether your fleet's CII needs managing. It is whether you'll manage it in July or discover it in December.