"Three months less one day" sounds like a rough guideline. It is not. It is a hard calculation - add three calendar months, subtract one day - and the result is a cliff edge. Miss it by a single day and your claim is typically out, no matter how strong your case.
Most people discover how strict this is at exactly the wrong moment. Here is what you need to know before that happens.
The standard rule: 3 months minus 1 day
For most employment tribunal claims - including unfair dismissal and discrimination - you have 3 months minus 1 day from the date the problem happened.
How the calculation works:
If your employment ended on 1 May, you add 3 calendar months (giving 1 August), then subtract 1 day. Your deadline is 31 July at 11:59pm.
Not "around the end of July." Not "within 3 months." Exactly 31 July.
Claims with longer limits (6 months)
Some claims get a longer window of 6 months minus 1 day:
- Statutory redundancy pay
- Equal pay claims
- Unfair dismissal connected to strike action
- Certain claims against trade unions
- Armed forces members' claims (in some circumstances)
If you are unsure which limit applies, assume the shorter one until you have confirmed otherwise.
The ACAS early conciliation requirement
Before you can submit a tribunal claim, you must in most cases contact ACAS for early conciliation and obtain an early conciliation certificate. There are limited exceptions (including some interim relief situations), but for the vast majority of claims this step is required - if you skip it, your claim will be rejected.
Here is where it gets helpful: contacting ACAS stops the clock on your time limit.
The "stop the clock" rule
The period between contacting ACAS and receiving your early conciliation certificate does not count towards your deadline. The clock pauses while ACAS tries to resolve the dispute.
Example: If you contact ACAS on day 60 of your 3-month window, and conciliation takes 4 weeks, you get those 4 weeks back. Your deadline extends by the length of the conciliation period.
The December 2025 change: 12 weeks instead of 6
As of 1 December 2025, the ACAS early conciliation period doubled from 6 weeks to 12 weeks. If you notified ACAS on or after 1 December, conciliation can last up to 12 weeks.
This means employers now face potentially longer uncertainty periods before a claim lands - but for claimants, it provides more time for settlement discussions without losing tribunal access.
The 1-month minimum guarantee
After early conciliation ends, you have at least 1 month to submit your ET1 claim form, even if your original deadline has passed.
This is a safety net, not a strategy. Do not rely on it.
The traps in the fine print
"Effective date of termination" is not always obvious
For unfair dismissal, time runs from the "effective date of termination" - your last day of employment. But this is not always the date you think it is:
- If you are dismissed without notice, it is the dismissal date
- If you work your notice, it is the last day of notice
- If you are paid in lieu of notice, it depends on contract terms
Practical takeaway: Get the termination date in writing and confirm exactly which day counts.
The problem date vs the discovery date
For discrimination claims, time runs from when the act happened - not when you realised it was discrimination. For ongoing discrimination, it runs from the last act in a series.
Practical takeaway: If discrimination was continuous, identify the last incident clearly.
Grievance procedures do not extend your deadline
Filing an internal grievance does not pause the tribunal clock. Your employer can take months to respond, and your deadline keeps ticking the whole time.
Practical takeaway: Contact ACAS early, even if you are still in an internal process.
The 7-day interim relief window
In some unfair dismissal situations - particularly trade union related or whistleblowing dismissals - you can apply for "interim relief" to keep your job pending the full hearing.
The catch: you have only 7 days from the effective date of termination.
Practical takeaway: If interim relief might apply, act immediately.
Coming in October 2026: 6-month time limits
The Employment Rights Act 2025 extends most employment tribunal time limits from 3 months to 6 months. This change is planned for no earlier than October 2026, subject to commencement orders. Some claims already have different limits, and commencement details will determine exactly which cases move to 6 months and when.
Once in force, the new 6-month limit applies to claims where time starts running on or after the implementation date.
Combined with the 12-week ACAS conciliation period, employers could face up to 9 months of uncertainty before receiving notice of a tribunal claim.
What to do first
- Calculate your deadline immediately - do not wait until you "feel ready"
- Contact ACAS early - this stops the clock and buys you time
- Do not rely on internal grievance procedures - they do not pause the deadline
- Get the termination date in writing - confirm exactly which day counts
- Keep records - screenshot emails, note dates, document everything
- Assume the shorter deadline until you have confirmed which limit applies
Need to calculate your exact deadline?
Use our calculator to work out key dates from your termination date. Note that employment tribunal limitation periods are calendar-based (not working-day-based), so the calculator helps you plan around the calendar-month rule and key milestones.
Calculate your deadline -> Open the calculator
Frequently Asked Questions
Q: What does "3 months less 1 day" actually mean? A: Add 3 calendar months to the relevant date, then subtract 1 day. If the event was on 15 March, 3 months later is 15 June, minus 1 day gives a deadline of 14 June.
Q: Does contacting ACAS extend my deadline? A: Yes. The time spent in ACAS early conciliation does not count towards your deadline. The clock stops while conciliation is ongoing.
Q: What if I miss the deadline? A: Tribunals can extend time limits, but the test depends on the claim type. For unfair dismissal and similar claims, the test is whether it was "not reasonably practicable" to present the claim in time. For discrimination claims, the tribunal has a broader "just and equitable" discretion to extend time. In either case, extensions are not guaranteed and "I did not know the deadline" is generally not sufficient on its own.
Q: Do bank holidays affect the deadline? A: The deadline is a calendar date. Do not assume an extension because of weekends or bank holidays - aim to lodge before the final day.
Conclusion
ACAS early conciliation genuinely stops the clock, and the 2026 changes will eventually double the standard window to 6 months. But until those changes take effect, the 3-month rule remains in force. The people who lose claims on time limits are almost never the ones with weak cases - they are the ones who assumed the deadline was approximate, or that an internal grievance would buy them time. It does not.
Sources & Further Reading:
- Acas - Employment tribunal time limits
- Acas - How early conciliation works
- Gov.uk - Make a claim to an employment tribunal
This guide is for informational purposes only and does not constitute legal advice. Always verify tribunal deadlines independently and seek legal advice if unsure.
