What Is the Carbon Intensity Indicator (CII)?
The Carbon Intensity Indicator (CII) is the IMO's operational efficiency measure under MARPOL Annex VI, in force since 1 January 2023. It rates how efficiently a ship transports cargo in terms of CO₂ emitted per unit of transport work, and assigns every applicable vessel an annual rating from A (major superior) to E (inferior).
CII applies to cargo, RoPax and cruise ships of 5,000 GT and above trading internationally — the same fleet already reporting fuel consumption under the IMO Data Collection System (DCS). Unlike EEXI, which is a one-time technical certification of the ship's design, CII is operational and annual: the same vessel can slide from C to D purely through how it is operated, chartered and maintained.
CII is verified from DCS fuel-consumption data submitted after each calendar year. The rating for operating year 2025 was confirmed on Statements of Compliance issued in 2026 — meaning decisions you make today are already writing next year's rating.
How Is CII Calculated? The AER Formula
Attained CII is calculated using the Annual Efficiency Ratio (AER), expressed in grams of CO₂ per deadweight-tonne-mile (dwt-nm):
Each fuel type has an emissions conversion factor (CF): HFO 3.114, MDO/MGO 3.206, LNG 2.750 tonnes CO₂ per tonne of fuel. Capacity is DWT for cargo ships and GT for cruise and RoPax vessels.
Worked Example
A 60,000 DWT bulk carrier consumes 5,200 t of HFO and 350 t of MGO over 52,000 nm in a calendar year:
- CO₂ emitted = (5,200 × 3.114) + (350 × 3.206) = 16,193 + 1,122 = 17,315 tonnes
- Transport work = 60,000 × 52,000 = 3.12 × 10⁹ dwt-nm
- Attained CII = 17,315,000,000 g ÷ 3.12 × 10⁹ = 5.55 g CO₂/dwt-nm
That attained value is then compared against the vessel's required CII — a ship-type-specific reference line reduced each year by the applicable reduction factor — and the ratio (attained ÷ required) determines the rating band.
CII Rating Bands & Reduction Factors Through 2030
Boundaries between bands are set by ship-type-specific dd vectors, so a C-rated bulker and a C-rated tanker sit at different absolute values but the same relative performance. What matters commercially:
| Rating | Meaning | Regulatory Consequence | Commercial Reality |
|---|---|---|---|
| A | Major superior | None — incentives encouraged | Preferred by cargo owners; green financing advantages |
| B | Minor superior | None | Strong charter market position |
| C | Moderate | Compliant baseline | Acceptable today; at risk as curve tightens |
| D | Minor inferior | 3 consecutive years → corrective action plan in SEEMP Part III | Charterer screening, higher scrutiny, weaker earnings |
| E | Inferior | Corrective action plan after a single year | Effective exclusion from many cargo programmes |
The Tightening Curve
| Year | Required Reduction vs 2019 Baseline |
|---|---|
| 2024 | 7% |
| 2025 | 9% |
| 2026 | 11% |
| 2027 | 13.625% |
| 2028 | 16.25% |
| 2029 | 18.875% |
| 2030 | 21.5% |
MEPC 83 (April 2025) locked in the post-2026 trajectory: the annual step nearly doubles from 2 to roughly 2.625 percentage points. A ship earning a mid-C rating today, operated identically, drifts into D territory around 2027–2028. Standing still is a downgrade strategy.
What Happens With a D or E Rating?
A vessel rated D for three consecutive years, or E in any single year, must develop a corrective action plan within its SEEMP Part III, showing how the required CII will be achieved, and have it verified before the Statement of Compliance is issued. Flag states and Recognised Organisations audit against this plan.
The sharper penalties are commercial. Major charterers embed CII thresholds in vetting; the Sea Cargo Charter aligns cargo-owner reporting with IMO trajectories; banks under the Poseidon Principles price climate alignment into lending. A poor rating narrows employment options precisely when freight markets reward flexibility. Layered on top sit EU ETS surrender obligations and FuelEU Maritime GHG-intensity penalties for European trading — carbon inefficiency now bills you three times.
7 Proven Strategies to Improve Your CII Rating
1. Voyage & Speed Optimisation
Fuel consumption rises roughly with the cube of speed. Trimming 1–1.5 knots on non-critical legs is the single fastest CII lever, often worth a full band. Integrated voyage planning and weather routing converts this from ad-hoc slow steaming into a repeatable, auditable practice.
2. Weather Routing
Dynamic routing around adverse currents, swell and wind typically saves 3–5% fuel per crossing. Modern routing engines re-optimise continuously against forecast updates rather than fixing a route at departure.
3. Hull & Propeller Management
Biofouling can add 15–35% to fuel consumption. Condition-triggered hull inspections, cleaning and propeller polishing — scheduled and evidenced through your planned maintenance system — protect both the rating and the TC description.
4. Engine & Auxiliary Efficiency
Worn injectors, fouled turbochargers, drifting SFOC and unnecessary auxiliary load quietly erode carbon intensity. Continuous performance monitoring against shop-test baselines catches degradation months before it shows in the annual DCS aggregate.
5. Port Call & Just-in-Time Arrival
Rushing to anchor is burned CII for zero transport work. Just-in-time arrival coordination with terminals converts waiting time into slower, cleaner steaming.
6. Energy-Saving Technologies
Propeller boss cap fins, pre-swirl ducts, air lubrication, wind-assist rotors and shaft generators deliver measurable AER gains; LED retrofits and VFD-driven pumps chip away at auxiliary load. Model payback against the 2027–2030 curve, not today's requirement.
7. Continuous Monitoring & Forecasting
The operators holding A–B ratings treat CII as a live KPI, not an annual surprise: noon-report or autolog data flows into a running attained-CII calculation, with end-of-year forecasts per vessel and alerts when a ship trends toward a band boundary while there is still time to act.
Where Software Makes the Difference
CII compliance is fundamentally a data discipline: fuel figures from the engine room, distances from the bridge, maintenance evidence from the PMS, voyage decisions from the chartering desk — all feeding one auditable number. Spreadsheets fracture exactly where verifiers look.
Volaxin Maritime Suite closes that loop natively: automated IMO DCS data capture with offline ship-side sync, live attained-CII tracking and year-end band forecasting per vessel, weather routing and voyage optimisation, and PMS-evidenced hull, propeller and engine efficiency management — with SEEMP Part III corrective actions tracked as verifiable workflows rather than documents in a drawer.
Turn CII from a compliance risk into a competitive edge
See how Volaxin tracks attained CII in real time, forecasts year-end ratings across your fleet, and links every efficiency action to auditable evidence.
Request a DemoFrequently Asked Questions
What is a good CII rating?
A, B and C are compliant. A and B signal superior efficiency and are increasingly demanded by charterers and financiers; C is the minimum acceptable — and a shrinking safe zone as reduction factors tighten each year.
Which ships must comply with CII?
Cargo, RoPax and cruise vessels of 5,000 GT and above on international voyages — the IMO DCS fleet.
What is the difference between EEXI and CII?
EEXI is a one-time technical standard for the ship's design; CII is an annual operational rating. A ship passes EEXI once, but must defend its CII every year.
What is the CII reduction factor for 2026?
11% below the 2019 reference line, rising to 13.625% in 2027 and 21.5% by 2030 following MEPC 83.
Can a D or E rated ship still trade?
Legally yes, subject to filing and following a verified corrective action plan. Commercially, D and E ratings increasingly mean charter exclusions and financing penalties.