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Attained vs Required EEXI: What It Means for Your Vessel

As global shipping regulations tighten to curb greenhouse gas (GHG) emissions, vessel owners and operators must keep pace with decarbonization efforts. One such regulation is the Energy Efficiency Existing Ship Index (EEXI), developed by the International Maritime Organization (IMO) to ensure that even existing ships operate more sustainably.
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This blog explores the importance of EEXI, defines attained and required EEXI, and offers formulas to help you calculate and compare them—so you can determine if your vessel is compliant or needs retrofitting for better energy performance.

Importance of EEXI

EEXI is a technical index that measures the energy efficiency of existing ships based on their design parameters. It aims to reduce CO₂ emissions by ensuring ships meet a minimum efficiency level, even if they were built before modern emission standards came into effect.

Starting January 1, 2023, all vessels above 400 gross tonnage must demonstrate EEXI compliance at their first annual, intermediate, or renewal survey. Non-compliance can lead to operational restrictions or even detention.

In essence, EEXI is not just a regulatory requirement—it’s a tool to future-proof your fleet against rising fuel costs, stricter emissions rules, and environmental pressure from stakeholders and cargo owners.

Why Attained and Required EEXI Matter

The comparison between attained EEXI and required EEXI helps assess whether a vessel is compliant.
  • Attained EEXI refers to your ship’s actual energy efficiency index, calculated from its technical specifications.
  • Required EEXI is the target benchmark set by IMO, based on your vessel’s type, size, and reference line values.

If your attained EEXI ≤ required EEXI, your ship complies.
If your attained EEXI > required EEXI, your vessel must take corrective action—such as engine power limitation (EPL), hull modifications, or adopting energy-saving devices.

This comparison is critical for compliance planning and operational efficiency.

What is Attained EEXI?

Attained EEXI represents the energy efficiency of a ship based on its existing design, propulsion system, and energy consumption at a reference speed. It is a one-time certification value unless major retrofits are made.

Attained EEXI helps determine how much CO₂ a ship emits per tonne-mile (g CO₂/tonne·nautical mile). The lower the value, the more efficient the vessel is.
Formula for Attained EEXI
The attained EEXI is calculated using the following IMO-defined formula:
EEXIattained =
CF × PME × SFCME + CF × PAE × SFCAE
Vref × DWT
Given Data:
  • CF = Conversion factor for fuel type (g CO₂/g fuel)
  • PME = Main engine power (kW)
  • SFCME = Specific fuel consumption of main engine (g/kWh)
  • PAE = Auxiliary engine power (kW)
  • SFCAE = Specific fuel consumption of auxiliary engines (g/kWh)
  • Vref = Reference speed of vessel (knots)
  • DWT = Deadweight tonnage (tonnes)
This formula quantifies emissions in terms of how much CO₂ is produced to transport one tonne of cargo one nautical mile.

What is Required EEXI?

Required EEXI is the benchmark index that a ship must meet to be considered compliant with IMO’s emission reduction goals. The required EEXI depends on:
  • Ship type (e.g., bulk carrier, tanker, container ship)
  • Ship size (measured in DWT or GT)
  • Reduction factor applied to the EEDI reference line for that vessel type and size
The IMO periodically reviews and updates these benchmarks to reflect global decarbonization efforts.
Formula for Required EEXI
The required EEXI is calculated using:
EEXIrequired = (1 − X) × EEDIref
Given Data:
  • X = Required reduction factor (expressed as a percentage)
  • EEDIref = Reference EEDI value for a specific vessel type and size
Each ship category has a baseline EEDI reference line derived from actual ship data, and IMO sets reduction rates (X) based on how much improvement is expected for each ship category.

Attained vs Required EEXI: What the Comparison Tells You

The real insight comes from comparing your ship’s attained EEXI against the required EEXI:
Parameter Attained EEXI Required EEXI
Purpose Actual efficiency based on current design Target benchmark for compliance
Based On Technical specs (engine, speed, fuel) IMO reference lines & reduction factors
Evaluation One-time, unless ship is modified Set by IMO for each vessel type
Compliance Must be ≤ required EEXI Determines minimum efficiency threshold

Why the Comparison Matters

  • Compliance Check:
    Ensures you meet IMO MARPOL Annex VI regulations.
  • Operational Planning:
    Helps evaluate the need for retrofits like engine power limitation or efficiency-enhancing technologies.
  • Cost Control:
    More efficient ships consume less fuel—lowering OPEX.
  • Emission Strategy:
    It’s a first step in your overall carbon reduction roadmap, including future CII (Carbon Intensity Indicator) planning.

Conclusion

EEXI compliance is a non-negotiable standard for shipowners operating in today’s maritime environment. Understanding and comparing your attained vs required EEXI helps you stay compliant, reduce emissions, and improve operational performance.

If your ship’s attained EEXI exceeds the required value, now is the time to act—whether through technical retrofits or operational limitations. Early compliance ensures smoother inspections, uninterrupted operations, and a stronger stance on sustainability.

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