What are the rules for extending a probation period in the UK?

Acas: tell the employee about the extension in writing and confirm it before the original probation period ends, because failing to do this could be a breach of contract, and update the written statement within one month. Agree the length, the review points, the expectations, the final review date and the possible outcomes.

Can you extend a probation period after it has ended?

Acas says the extension must be confirmed before the original probation period ends and that failing to do this could be a breach of contract. For a six-month probation that started on 1 February 2027, the last day to confirm it is 31 July 2027.

How long can a probation extension be?

No law sets a length. Acas says there is no legal requirement to have a probation period and that it can be any length; the length of an extension is one of the points Acas says to agree with the employee.

Does extending probation delay unfair dismissal rights?

No. Protection depends on continuous service up to the effective date of termination: 6 months when that date is on or after 1 January 2027, two years before it. For a start on 1 February 2027 protection starts on 31 July 2027 whether or not probation is extended.

Do I have to update the contract when I extend probation?

Acas says to update the written statement within one month. The extension itself is confirmed in writing before the original probation period ends.

Probation extension rules (UK): in writing, before it ends

The probation extension rules in the UK, from Acas: tell the employee about the extension in writing, confirm it before the original probation period ends, then update the written statement within one month. For a six-month probation that started on 1 February 2027, that means confirming it in writing by 31 July 2027, the last day of the original probation. The extension does not move the date unfair dismissal protection starts: 31 July 2027.

Open the probation review planner

The rules, from Acas

These are the probation extension rules Acas sets out:

Tell the employee about the extension in writing.
Confirm it before the original probation period ends. Acas says failing to do this could be a breach of contract.
Update the written statement within one month.
Agree the length, the review points, the expectations, the final review date and the possible outcomes.

Acas also says there is no legal requirement to have a probation period and that it can be any length, so no statute sets a maximum length for an extension or a number of extensions. What the contract or probation policy says still applies.

Letter deadline and new end date: start 1 February 2027

The letter deadline is the last day of the original probation. The new end date counts from the start date like the original one: the period of months that begins with the first day of work.

Start Mon 1 Feb 2027, one week's notice worked, protection from Sat 31 Jul 2027
Original probation	Letter by	Extended by	New end	Last notice day	New end after it?
3 months	Fri 30 Apr 2027	1 month	Mon 31 May 2027	Fri 23 Jul 2027	No
3 months	Fri 30 Apr 2027	2 months	Wed 30 Jun 2027	Fri 23 Jul 2027	No
3 months	Fri 30 Apr 2027	3 months	Sat 31 Jul 2027	Fri 23 Jul 2027	Yes
6 months	Sat 31 Jul 2027	1 month	Tue 31 Aug 2027	Fri 23 Jul 2027	Yes
6 months	Sat 31 Jul 2027	2 months	Thu 30 Sep 2027	Fri 23 Jul 2027	Yes
6 months	Sat 31 Jul 2027	3 months	Sun 31 Oct 2027	Fri 23 Jul 2027	Yes

Where the new end falls after the last notice day, a decision at the end of the extended probation comes on or after 31 July 2027, when protection has started. A dismissal then needs a fair reason and a fair procedure like any other. Acas says ending probation before protection starts does not avoid legal risks either.

What an extension does not change

The protection date. Unfair dismissal protection depends on continuous service up to the effective date of termination: 6 months when that date is on or after 1 January 2027 (s.108(1); SI 2026/559 reg. 4). For a start on 1 February 2027 it is 31 July 2027 in every row of the table. More in Unfair dismissal 6 month rule from 1 January 2027.
The last day to give notice. For the qualifying period, s.97(2) of the Employment Rights Act 1996 adds the statutory notice week to the effective date of termination, so with one week's notice the last day is 23 July 2027, 8 days before protection starts. See the statutory notice week guide.
The Employment Rights Act 2025 does not change the existing day one protections against discrimination and automatically unfair grounds for dismissal.

What to put in the extension letter

From the points Acas lists for an extension:

the new end date and the length of the extension;
the review points during the extension;
the expectations the employee has to meet;
the date of the final review;
the possible outcomes.

Have regular formal reviews during the probation period and a final review to discuss the outcome; keep records and share them with the employee after each meeting. If the extended probation is not passed: Dismissal during probation should be a last resort. Follow a fair procedure, give the reasons in writing and give the correct notice: the statutory minimum or the contractual notice.

Put your own start date in the probation review planner to get the letter deadline, the review dates and the last notice day. For how probation lengths sit against the protection date, see probation periods under the six-month rule. Pro adds letter templates for each outcome (passed, extended, not passed): templates, not legal advice.

Sources

Extending probation (Acas): Acas, Probation periods: Extension — https://www.acas.org.uk/probation-periods/extension, read on 2026-09-30
Probation (Acas): Acas, Probation periods: What probation is (last updated 24 July 2026) — https://www.acas.org.uk/probation-periods, read on 2026-09-30
Reviews (Acas): Acas, Probation periods: Reviews — https://www.acas.org.uk/probation-periods/reviews, read on 2026-09-30
Failing probation (Acas): Acas, Probation periods: Dismissal — https://www.acas.org.uk/probation-periods/dismissal, read on 2026-09-30
Six-month rule starts: The Employment Rights Act 2025 (Commencement No. 4 and Transitional and Saving Provisions) Regulations 2026 (SI 2026/559), reg. 3(a): section 25 of the 2025 Act comes into force on 1st January 2027 — https://www.legislation.gov.uk/uksi/2026/559/made, read on 2026-09-30
Qualifying period: Employment Rights Act 1996, s.108(1): "not less than two years ending with the effective date of termination" — https://www.legislation.gov.uk/ukpga/1996/18/section/108; Employment Rights Act 2025, s.25(2)(a): in s.108(1) "for 'two years' substitute 'six months'" — https://www.legislation.gov.uk/ukpga/2025/36/section/25, read on 2026-09-30
Which rule applies: SI 2026/559, reg. 4(1)(a) and (b); "effective date of termination" has the meaning in s.97 of the 1996 Act (reg. 4(2)) — https://www.legislation.gov.uk/uksi/2026/559/made, read on 2026-09-30
Statutory notice extension: Employment Rights Act 1996, s.97(2) and (3) — https://www.legislation.gov.uk/ukpga/1996/18/section/97, read on 2026-09-30
Day-one protections: GOV.UK Factsheet: Unfair Dismissal — https://assets.publishing.service.gov.uk/media/6a049a3d22977ebc82cb3f1a/unfair-dismissal-factsheet.pdf; Acas, Probation periods: "Other employment protections apply during probation. For example: discrimination, whistleblowing, breach of contract" — https://www.acas.org.uk/probation-periods, read on 2026-09-30

Frequently asked questions

What are the rules for extending a probation period in the UK?: Acas: tell the employee about the extension in writing and confirm it before the original probation period ends, because failing to do this could be a breach of contract, and update the written statement within one month. Agree the length, the review points, the expectations, the final review date and the possible outcomes.
Can you extend a probation period after it has ended?: Acas says the extension must be confirmed before the original probation period ends and that failing to do this could be a breach of contract. For a six-month probation that started on 1 February 2027, the last day to confirm it is 31 July 2027.
How long can a probation extension be?: No law sets a length. Acas says there is no legal requirement to have a probation period and that it can be any length; the length of an extension is one of the points Acas says to agree with the employee.
Does extending probation delay unfair dismissal rights?: No. Protection depends on continuous service up to the effective date of termination: 6 months when that date is on or after 1 January 2027, two years before it. For a start on 1 February 2027 protection starts on 31 July 2027 whether or not probation is extended.
Do I have to update the contract when I extend probation?: Acas says to update the written statement within one month. The extension itself is confirmed in writing before the original probation period ends.

Probation periods under the six-month rule
A six-month probation now ends on the day unfair dismissal protection starts. Probation end dates, last notice days and review points for 3 to 6 months.
Unfair dismissal 6 month rule from 1 January 2027
From 1 January 2027 unfair dismissal needs six months' service, not two years. Started on or before 2 July 2026? Protected that day. Table by start date.
Why acting at five months may be too late: the statutory notice rule
Section 97(2) adds the one-week statutory notice to the effective date of termination, so notice at five months and three weeks can land after protection starts.
Unfair dismissal time limit: 6 months from 1 October 2026
Tribunal claims for unfair dismissal: six months beginning with the effective date of termination when it falls on or after 1 October 2026, three before. Worked dates.

Last updated 2026-10-04. Date calculator and templates based on the Employment Rights Act 1996 as amended by the Employment Rights Act 2025. Not legal advice. Continuity rules have exceptions; check with Acas or a solicitor before dismissing anyone. Not affiliated with Acas or the UK Government.