What are the ESOS thresholds?

An organisation qualifies if it, or any UK undertaking in its group, has 250 or more employees, or has an annual turnover over £44 million and a balance sheet total over £38 million, on the qualification date. For Phase 4 that date is 31 December 2026.

When is the ESOS Phase 4 deadline?

You must notify compliance by 5 December 2027. Your Phase 4 action plan is then due by 5 December 2028, with progress updates in 2029 and 2030.

Does ESOS apply to SMEs?

Not on their own. But a small company that is part of a group containing a large UK undertaking is included in the group's ESOS assessment.

Is ESOS the same as SECR?

No. SECR is annual reporting of energy and emissions in your annual report. ESOS is a four-yearly energy audit that identifies ways to save energy, notified to the Environment Agency or the regulator for your nation. Many large companies are in both.

Can ISO 50001 replace an ESOS audit?

Yes. ISO 50001 certification covering at least 95% of your total energy use is a route to compliance and removes the need for a lead assessor. Display Energy Certificates and Green Deal Assessments are no longer accepted as routes in Phase 4.

Do I need a lead assessor?

Yes, unless your total energy consumption is under 40,000 kWh, you use no energy at all, or ISO 50001 covers at least 95% of your energy.

ESOS Phase 4: who qualifies, the deadlines and what you must do

ESOS, the Energy Savings Opportunity Scheme, requires large UK undertakings (250 or more employees, or turnover over £44 million and a balance sheet over £38 million) to audit their energy use every four years. For Phase 4, the qualification date is 31 December 2026 and the deadline to notify compliance is 5 December 2027, followed by an action plan by 5 December 2028.

Updated 3 October 2026 by the Carbon Recycling team. Figures use the official UK government conversion factors and are checked against the current gov.uk guidance.

Who has to comply?

You must take part if, on the qualification date of 31 December 2026, your organisation or any UK undertaking in its group is a large undertaking:

250 or more employees, counting employees, owners, managers and partners, averaged across the year, or
annual turnover over £44 million and a balance sheet total over £38 million, both together.

The thresholds are unchanged from Phase 3. An undertaking keeps its status until it falls on the other side of the thresholds for two consecutive accounting periods, so one unusual year does not take you in or out. Groups take part as a whole: if one UK company in the group qualifies, the group's UK undertakings are assessed together. UK establishments of overseas companies can also be caught. Public bodies are not covered.

ESOS uses different thresholds from SECR, which still uses the earlier Companies Act definition of large (250 employees, £36 million turnover, £18 million balance sheet, two out of three). Our SECR checker covers that side.

The Phase 4 dates

Milestone	Date
Compliance period	6 December 2023 to 5 December 2027
Qualification date	31 December 2026
Phase 3 action plan progress update (Phase 3 participants)	5 December 2026
Notification of compliance	5 December 2027
Phase 4 action plan	5 December 2028
Phase 4 progress updates	2029 and 2030

Your total energy consumption is measured over a reference period of 12 consecutive months that includes the qualification date and ends before the compliance date. A calendar year 2026 or a financial year to March 2027 would both work.

What you have to do

Measure total energy consumption for the reference period, across buildings, transport and industrial processes, in kWh. That includes fuel in vehicles you operate.
Identify areas of significant energy consumption covering at least 95% of the total. The remaining 5% can be left out.
Calculate energy intensity ratios for buildings (for example kWh per square metre), transport (for example kWh per mile), industrial processes (kWh per unit of output) and other uses.
Choose your route to compliance: ESOS energy audits of the significant areas, or ISO 50001 certification. Audits must use 12 months of verifiable data and identify cost-effective energy saving opportunities.
Appoint a lead assessor to carry out or review the assessment, unless you are exempt (see the FAQ).
Review your Phase 3 action plan, if you had one, and explain any measures you did not implement.
Get directors to review the findings and confirm compliance, then notify the regulator through the online MESOS system by 5 December 2027, and keep an evidence pack.
Publish an action plan of the measures you will take, by 5 December 2028, and report progress each year after.

Who regulates ESOS?

The Environment Agency is the scheme administrator and regulates England. Natural Resources Wales, the Scottish Environment Protection Agency and the Northern Ireland Environment Agency regulate their nations, and DESNZ covers offshore activities. Regulators can issue civil penalties for non-compliance and publish a summary of the penalties they have imposed.

ESOS and your carbon reporting

ESOS is about energy, not carbon, but the data overlaps heavily. The kWh of gas, electricity and transport fuel you collect for ESOS are the same figures behind your SECR report and your Scope 1 and 2 emissions. Collecting them once, on the same 12-month period, saves work. The opportunities an ESOS audit finds are also ready-made projects for a Carbon Reduction Plan or a net zero plan. Our kWh to CO2e calculator turns your ESOS energy totals into emissions.

What may change

The government's Modernising Corporate Reporting consultation, published in September 2026, says DESNZ intends to consult on SECR and ESOS later in 2026, building on an evaluation of SECR and an evaluation of ESOS that is under way. Phase 4 dates and rules are not affected by that. We will update this guide if anything changes.

How Carbon Recycling helps

Carbon Recycling records energy and fuel by site, vehicle and month, with kWh calculated for every fuel, so your ESOS total energy consumption and your SECR figures come from one set of data. It does not replace your lead assessor or audit, but it gives them clean, complete energy data to start from.