ESOS deadlines: every date, and the rule behind it

Regulation 4(2) opens each compliance period on the 6th December after the last one ends, and closes it on the 5th December four years later.

The compliance date is the last day of the period, and the qualification date is the 31 December immediately before it, eleven months and five days earlier.

Phase 1 is the only short period: it began when the Regulations came into force on 17 July 2014 and ran to 5 December 2015.

Phase 3’s compliance date is the only one that is neither a 5 December nor a 31 December: it was extended by six months to 5 June 2024.

The extension did not move the Phase 4 clock, which started on 6 December 2023, so for six months organisations were inside Phase 4 while still working to a Phase 3 date.

SI 2026/701 did not amend regulation 4, and the Environment Agency’s Phase 4 guidance restates 5 December 2027 as the Phase 4 compliance date.

Which ESOS deadline applies depends on where you stand in two overlapping cycles, so the quickest answer starts from a date.

The finder beside this text places any day from 17 July 2014 to 5 December 2035 in its compliance period and lists the next dated duties after it, each with its provision.

On 30 September 2026 it shows Phase 4, with the Phase 3 further progress update next, then Phase 4 qualification, then the Phase 4 notification.

A group that was not in Phase 3 has no 5 December 2026 duty, and its first ESOS date is the 31 December 2026 qualification test.

A group that was in Phase 3 but will not be large on 31 December 2026 still owes the Phase 3 update, and should tell its regulator it does not qualify for Phase 4.

A group in both carries the Phase 3 plan into its Phase 4 report, which must review it under regulation 27E.

Every date after a compliance date comes from Part 6A, inserted by SI 2023/1182.

Regulation 34A(10) makes the “relevant compliance period” the one following the period the notification related to, and each window runs from an anniversary of its first day.

For a Phase 4 notification the relevant period is 6 December 2027 to 5 December 2031, so the plan is due by 5 December 2028 and the updates by 5 December 2029, 2030 and 2031.

The third update is new: SI 2026/701 regulation 28 inserted it for compliance periods ending on or after 5 December 2027.

The Environment Agency’s Phase 4 guidance describes the Phase 4 updates as falling “in 2029 and 2030” in its stages list and names three elsewhere; the Regulations say three.

Each date is the last day of a window, so a plan or update may be filed at any point inside it; the ESOS action plan page covers what the plan must say.

Every ESOS filing goes through MESOS, the Environment Agency’s online service, which the Regulations call the Notification System.

MESOS opened for Phase 3 registration on 19 March 2024 and for notifications on 30 April 2024, replacing the survey tool used in the first two phases.

The Phase 4 guidance says further information on submitting the Phase 4 notification will be provided, and that there is no charge for submitting it.

Publication runs on its own clock under regulation 10(2), and the guidance gives 10 June 2028 as the Phase 4 publication date.

The notification and the ESOS notification page go into what is asked for; the ESOS reporting page what is published.

The qualification date is a single day, but the figures tested on it come from a whole financial year.

Schedule 1 uses the accounts for the financial year ending on the qualification date or in the twelve months immediately before it, and the headcount is averaged month by month over that same year.

For a calendar-year company that is the year ending on 31 December 2026 itself, whose accounts will not be finished until well into 2027, so the test may first be run on management figures and confirmed later.

For a company with a March year end it is the year to 31 March 2026, already closed, which is the Environment Agency’s own worked example.

Where an undertaking is close to the line or has recently grown or shrunk, Schedule 1 paragraph 11 requires looking back to the last two consecutive accounting periods at the same size, however far back that is.

The guidance gives two five-year patterns to show the effect: a company large in 2022 and 2023, small in 2024 and 2025 and large again in 2026 is not in scope, while one large in 2022 and 2023, small in 2024, large in 2025 and small in 2026 still is.

Missing the compliance date can trigger two offences: failing to notify under regulation 43, and failing to carry out an assessment under regulation 45.

The daily limb does not run from the compliance date itself: the guidance says it runs from the day after the relevant notice is served until the breach is remedied, capped at 80 working days.

That gives statutory ceilings of £45,000 for failing to notify and £90,000 for failing to carry out an assessment, each with publication of the undertaking’s name, the requirement breached and the amount.

The regulators work through three notices: a compliance notice asking for information, an enforcement notice saying what must be done, and a penalty notice imposing the penalty.

For a new entrant in its first compliance period, the Environment Agency’s Annex 2 says it will normally cap the initial penalty for failing to audit at £5,000.

Missing an action plan or progress update date carries no penalty; Part 8 does not name those duties, and the failure is published instead.

Any determination or notice can be appealed on an error of fact, an error of law or unreasonableness, to the First-tier Tribunal for England, Wales and offshore, the Scottish Ministers, or the Planning Appeals Commission in Northern Ireland.

The calculator beside this text shows how the fixed and daily limbs combine for each offence.