Every rule this calculator applies, and where it comes from.

The calculator does not estimate. It applies named provisions, in a fixed order, and shows its working on screen. This page names each one so you can check it — or hand it to an adviser who will.

What it answers is when, not whether. It works out the date by which a claim must reach the tribunal. It does not decide whether you have a claim, how strong it is, or whether a tribunal would extend time. England & Wales only.

The time limit

Unfair dismissal — s.111(2) Employment Rights Act 1996. The claim must be presented before the end of three months beginning with the effective date of termination. That is why the answer is three months less one day: a period “beginning with” a date includes that date. Read s.111

Discrimination — s.123(1) Equality Act 2010. Three months starting with the act complained of, measured the same way. For a series of related acts the period runs from the last of them. Read s.123

ACAS early conciliation — the stop-the-clock

Before bringing most claims you must notify ACAS. That process pauses the limitation clock, and it is where most miscalculations happen. s.207B Employment Rights Act 1996 governs it for ERA claims and s.140B Equality Act 2010 for discrimination claims. The two are mechanically identical — same Day A, same Day B, same subsections — so the calculator implements the mechanism once and it serves both.

Day A is the day ACAS received your notification. Day B is the day the certificate was issued.

s.207B(3) — the days from the day after Day A up to and including Day B do not count towards the limit. The clock stops for the length of conciliation. Read s.207B · Read s.140B

s.207B(4) — a floor, not an extension. If the limit would otherwise expire in the month after Day B, you get until one month after Day B instead. The calculator applies whichever of the two produces the later date, and says which one it used.

The two cases that decide the edges

Raison v DF Capital Bank [2025] EAT 86. Where ACAS was notified before the effective date of termination, only the conciliation days falling after that date are counted; earlier days are disregarded. The judgment’s own worked example — EDT 17 February, Day A 13 February, Day B 28 February, giving eleven countable days — is a test case in this codebase, so the calculator is checked against it on every change.

Dodds v Walker [1981] 1 WLR 1027. The corresponding-date rule for measuring months. Three months from 30 November is 28 or 29 February, because there is no 30 February — the period ends on the last day of the month instead. Month-end dates are where naive date arithmetic silently loses a day.

The change on 1 October 2026

The Employment Rights Act 2025 extends the primary period from three months to six for acts or failures falling on or after 1 October 2026. Anything arising wholly before that date keeps three months less one day. Early conciliation continues to pause the clock exactly as before.

The calculator applies whichever regime your date falls under and states which one in its working, so you are never left guessing which rule produced the answer.

What this calculator does not do

It does not tell you whether you have a claim. That is a different question with a different answer, and one dated change makes the distinction sharper: on 1 January 2027 the qualifying period for ordinary unfair dismissal falls from two years’ service to six months. That is a change to eligibility, not to the time limit, and this tool takes no account of it. Two separate six-month changes, on two different dates, to two different things. ACAS on the 2025 Act

It also does not decide whether a tribunal would extend time. Tribunals have a discretion to allow a late claim in limited circumstances, and nothing here should be read as saying a missed deadline is always fatal — only that it very often is.

If any of this matters to a decision you are about to make, speak to ACAS, Citizens Advice, a trade union or a solicitor.

Corrections

If you think a rule here is applied wrongly, please say so — it is the most useful message this project can receive. ask@fairform.app

Last reviewed 9 September 2026. Fairform provides information and tools, not legal advice.