# EEXI | Navatom Maritime Glossary
The Energy Efficiency Existing Ship Index (EEXI) is a one-time technical measure under MARPOL Annex VI. It sets a mandatory baseline energy efficiency standard for existing ships. Ships must comply from their first annual, intermediate or renewal IAPP survey on or after 1 January 2023.

URL: https://navatom.com/glossary/eexi

## Synonyms
- Energy Efficiency Existing Ship Index
- EEXI Rating

## Definition
## What Is EEXI?
The Energy Efficiency Existing Ship Index (EEXI) is a regulatory measure adopted by the IMO under amendments to MARPOL Annex VI that entered into force on 1 January 2023. While the Energy Efficiency Design Index (EEDI) applies to new-build ships, EEXI extends a similar energy efficiency baseline requirement to existing vessels.
Every ship of 400 GT and above falling under MARPOL Annex VI must calculate its attained EEXI value and demonstrate that it meets or falls below the required EEXI threshold for its ship type and size category.
## How EEXI Is Calculated
The EEXI calculation formula is adapted from the EEDI methodology and expresses a ship's energy efficiency in grams of CO2 per tonne-mile of transport work. The attained EEXI is determined using the ship's installed engine power, specific fuel oil consumption, and design parameters.
The required EEXI is set as a percentage reduction factor below a reference line established for each ship type. If a vessel's attained EEXI exceeds the required value, the ship must implement technical modifications to bring it into compliance.
## Compliance Options
Ship owners have several technical options to achieve EEXI compliance. Engine Power Limitation (EPL) is the most common and cost-effective approach, using either a shaft or overridable power limitation to reduce the maximum continuous rating of the main engine.
Other options include waste heat recovery systems, energy-saving devices such as propeller boss cap fins or air lubrication systems, and in some cases switching to lower-carbon fuels. Unlike CII, which measures ongoing operational performance, EEXI is a one-time technical certification — once a ship demonstrates compliance, no annual recalculation is required unless the vessel undergoes significant modifications.
EEXI and CII together form the IMO's short-term greenhouse gas reduction strategy. While EEXI sets the technical floor for energy efficiency through design and equipment, CII drives continuous operational improvement through voyage optimization, speed management, and fuel monitoring.
Ship management platforms help operators understand the interplay between these two measures, model the impact of different compliance strategies, and maintain the documentation required for IAPP survey verification.

## Related Terms
- [CII Rating](https://navatom.com/glossary/cii-rating) — The Carbon Intensity Indicator (CII) is an IMO operational measure of how efficiently a ship carries cargo for the CO2 it emits. Each ship gets a rating from A to E, on a scale that tightens every year.
- [SEEMP](https://navatom.com/glossary/seemp) — The Ship Energy Efficiency Management Plan (SEEMP) is a mandatory operational plan under MARPOL Annex VI. Shipping companies use it to manage and improve the energy efficiency of their vessels over their whole working life.
- [MARPOL Annex VI](https://navatom.com/glossary/marpol-annex-vi) — MARPOL Annex VI is the part of the MARPOL convention that limits air pollution from ships. It was adopted in 1997 and has been in force since 2005. It limits sulphur oxide, nitrogen oxide and ozone-depleting emissions. Its energy efficiency rules include the EEXI, the CII and the SEEMP.