ESOS Deadlines: Phase 3 and Phase 4 Key Dates

The short answer. Your next ESOS deadline is 5 December 2026, the second Phase 3 annual progress update. Phase 4 compliance follows on 5 December 2027, with qualification assessed on 31 December 2026.

ESOS runs on a four-year cycle, but the obligations do not arrive only once every four years. Phase 3 introduced an action plan and annual progress updates, so most qualifying organisations now have something due most years.

This page sets out every date that still matters, and what each one actually requires.

The dates

Requirement	Date	Status
Phase 3 notification of compliance	5 June 2024	Passed
Phase 3 action plan	5 December 2024	Passed
First Phase 3 annual progress update	5 December 2025	Passed
Second Phase 3 annual progress update	5 December 2026	Next
Phase 4 qualification date	31 December 2026	Upcoming
Phase 4 compliance deadline	5 December 2027	Upcoming

The next deadline: 5 December 2026

For most organisations that qualified for Phase 3, this is the obligation that comes next, and it is the one most often overlooked.

The second annual progress update reports what you have done against the commitments in your Phase 3 action plan. It must record which measures were implemented, the estimated energy savings in kWh, and an explanation where planned measures were not completed as expected.

Two practical points. It must be approved by a board-level director or equivalent, so it needs to be on somebody's agenda before December rather than during it. And it is submitted through the government's Manage your ESOS reporting service, so whoever holds the login needs to be findable.

If your action plan has sat untouched since 2024, that is common and it is not fatal. The update reports what happened, including where measures were not implemented and why. Reporting honestly is the requirement. Implementing everything is not.

The Phase 4 qualification date: 31 December 2026

Qualification is assessed on this date, not on your size when the assessment is carried out. That distinction catches people out.

An organisation that grows past the threshold in November 2026 qualifies. One that shrinks below it in January 2027 still qualifies, because the test was already met.

The Phase 4 thresholds are unchanged from Phase 3, and the guidance published on 22 July 2026 confirms them. An organisation qualifies if it employs 250 or more people, or has an annual turnover in excess of £44 million together with an annual balance sheet total in excess of £38 million. The government decided not to align the thresholds with Streamlined Energy and Carbon Reporting.

Corporate groups are assessed at group level. A small UK company inside a large group can be in scope on its own account.

The Phase 4 compliance deadline: 5 December 2027

By this date, qualifying organisations must have completed their assessment and submitted notification to the Environment Agency.

Two years sounds comfortable. In practice the timeline compresses for three reasons.

You need twelve months of energy data. If your metering is poor, the data exercise has to happen before the assessment can start, which pushes the real start date back considerably.

Lead Assessor capacity gets scarce. Everyone leaves it, then everyone needs an assessor in the same six months. Booking early costs less and gives you more choice.

The audits need to be worth doing. An assessment rushed to meet a deadline produces a compliant report and nothing else. One with time in it identifies savings that pay for the exercise.

What the 2026 amendment regulations changed

The Energy Savings Opportunity Scheme (Amendment) Regulations 2026 came into force on 22 July 2026 and added requirements for the compliance period ending in 2027:

• removal of Display Energy Certificates and Green Deal Assessments as compliance routes, leaving energy audits and ISO 50001 certification as the only options
• a wider ISO 50001 exemption. Certification covering either your total energy consumption or your significant energy consumption now exempts you from appointing a Lead Assessor and from producing an ESOS report. In Phase 3 that exemption applied only where certification covered the whole of your total energy consumption
• reporting the energy savings achieved during the compliance period, with a description of each measure, the saving it delivered, and its category, such as behaviour change, training or capital investment
• reviewing the previous action plan, listing any measures that were not implemented and explaining why
• an additional, final annual progress update
• Lead Assessors must notify their professional body of each assessment they complete or review, along with the participant's contact details, so the body can seek consent to quality-check the report
• the notification of compliance must now include the number of sites covered by energy audits and your ISO 50001 certification details, both voluntary in Phase 3, and UK SIC codes in place of international ones

The additional savings and action plan detail goes into your ESOS report and notification of compliance, but is not published.

For a side by side comparison of the two phases, see ESOS Phase 3 vs Phase 4: what actually changed.

Check the date on anything you read. The updated ESOS guidance was published on 22 July 2026. Phase 3 summaries, including some still published by consultancies, no longer describe the current requirements accurately.

What happens if you miss a deadline

Environmental regulators can investigate and impose civil sanctions, including financial penalties and publication penalties. Penalties are published, so there is a reputational element as well as a financial one.

Missing a deadline does not remove the obligation. If you have missed one, check current guidance, complete the outstanding work and contact the relevant regulator rather than waiting to be contacted.

Where to go next

For what ESOS is and who it applies to, see our ESOS guide. To check whether you are in scope, read Do you qualify for ESOS Phase 4?. If you want help with the December 2026 update or the Phase 4 assessment, see our ESOS compliance services.