TL;DR: UK probation periods are purely contractual — no statute sets a minimum or maximum, and nothing obliges you to have one. From 1 January 2027 the unfair dismissal qualifying period drops to six months, which puts the UK's most common probation length right on top of the new threshold, so probation length, extension mechanics and review timing all need redesigning now.
What UK law actually says about probation (almost nothing)
Probation is a creature of contract. It appears nowhere in the Employment Rights Act 1996, and no other statute sets a minimum length, a maximum length, or any obligation to run one at all. Acas is explicit about this: a probation period exists only because the employment contract says it does.
That matters because of what probation therefore cannot do. It changes your internal process, and in many UK contracts it shortens the notice either side has to give during the period. It does not change the employee's statutory rights by a single day.
So can an employer dismiss someone during probation without running a full procedure? Usually yes, and the probation clause has nothing to do with it. Ordinary unfair dismissal protection only starts once the employee has the qualifying period of service, two years now and six months from 1 January 2027, so below that threshold the employer does not have to establish a fair reason or follow a fair procedure to defend an ordinary unfair dismissal claim. What that has never covered is a reason that is discriminatory or automatically unfair, and it does not remove the obligation to give the correct notice, contractual or statutory.
Those rights apply from day one and run right through probation. National Minimum Wage. Paid holiday under the Working Time Regulations 1998. SSP eligibility once the qualifying conditions are met. Discrimination protection under the Equality Act 2010. None of them wait for a probation review to be signed off.
The same is true of the automatically unfair dismissal reasons that need no minimum service: pregnancy and maternity, family leave, a flexible working request, whistleblowing, asserting a statutory right, health and safety, trade union activity, jury service. The Employment Rights Act 2025 adds dismissal-and-rehire to that list. A dismissal in week three for any of those reasons is as actionable as one in year five, and the 2027 reform does not touch them because they never had a qualifying period to reduce.
So the framing for everything below is this. Probation has never been a legal shield. It is a management process that happened to sit comfortably inside a two-year window, and that window is closing on 1 January 2027.
How long can a probation period be, and how long should it be?
There is no legal maximum. If you came here for that answer, that is the whole answer, and any source that gives you a number is describing what employers do, not what the law requires.
Common practice is still useful. Three and six months are the standard UK choices. Around 40% of UK businesses operate a discretionary probationary period, and the large majority of those run to six months or less, according to ONS Business insights data (Wave 133) cited in the Department for Business and Trade's unfair dismissal factsheet.
Employees often ask whether six months is unreasonable, and the honest answer is no. It is lawful, it is the most common arrangement in the country, and length alone tells you nothing about fairness. A six-month probation with written objectives and three recorded reviews is fairer than a three-month one where nobody says anything until the last week.
Acas's own position cuts against the advice currently circulating. It notes that six months or less might not be appropriate for all roles, particularly technical or specialist posts where someone needs longer training before anyone can make a fair judgement about their work.
Hold onto that, because the advice in question is to shorten probation to roughly three months. That recommendation comes from employment law firms reading the new timetable, not from Acas and not from government. No regulator has published a recommended number, and anyone telling you otherwise is paraphrasing a law firm article.
The real design question is not length in isolation. It is whether a decision can be made, reviewed, communicated and actioned, notice included, before the employee crosses six months' service.
Extending probation without breaching the contract
One mechanical rule governs extensions, and it is the rule most often broken. The extension must be confirmed in writing before the original probation period ends. A letter or an email will do. Acas warns that missing that deadline could be a breach of contract. Once the original period has expired, the employee has a strong argument that they completed probation on its original terms.
The written statement of employment particulars also has to be updated within one month of the change. That is a separate obligation from the extension letter itself, and it is routinely forgotten.
Acas sets out what the extension should actually say, and it is more than a new date. Agree the length of the extension, the review checkpoints inside it, the specific improvement expected, the support or training you will provide, the final review date, and the possible outcomes at the end of it. An extension with no new checkpoints is just a delay with paperwork attached.
The contract has to give you the right to extend in the first place. If it is silent on extension, you are not exercising a clause. You are asking the employee to agree a variation to their contract, and they can decline.
That distinction has teeth. A botched or unilateral extension is precisely the territory where a unilateral change can amount to a fundamental breach, which opens a different claim on a different footing. Pursued as a breach of contract claim, it has never required any minimum service at all. Pursued as constructive unfair dismissal, it needs the same qualifying service as an ordinary unfair dismissal claim, which is exactly what shortens on 1 January 2027.
A worked probation policy you can adapt
What follows is constructed from the Acas building blocks: clear expectations from day one, formal and informal reviews, a written extension process, a dated final review. No authoritative template exists, Acas does not publish one, and this is a starting point to adapt to your roles rather than a compliant policy you can adopt unread.
Length. Three months as the default. Keep a documented exception process for roles where a fair assessment genuinely takes longer, which is Acas's point about technical and specialist posts. The reasoning matters more than the number: three months leaves room to extend once and still reach a decision, serve notice and finish before six months' service.
Review cadence. The shape that produces an unsurprising decision looks like this:
- Written objectives issued in week one, before anyone is being measured against anything.
- Formal reviews at week 4, week 8 and week 11, each one recorded in writing and the record shared with the employee.
- Informal check-ins weekly or fortnightly in between, which is where problems surface early enough to fix.
Final review timing. This is the single design decision that matters most, and it is the one most policies get wrong. The final review has to sit with enough runway left to act on the outcome, including serving notice. Acas's standard is that the result should never come as a surprise, and a review held the day before the end date fails that test even when the paperwork is immaculate.
Extension. One extension only, confirmed in writing before the original end date, with its own checkpoints and its own final review date. Set its length so that the final review and any notice complete before six months' service. On a three-month default that means no more than two months.
Notice during probation. Set the contractual notice out explicitly for the probation period and for after it. Statutory minimum notice under section 86 of the Employment Rights Act 1996 bites from one month's service at one week from the employer, and a contract can improve on that but never undercut it. Below one month's service, no statutory notice applies either way.
Outcomes. Define them up front: pass, extend, or dismiss. Name who decides each one and what evidence they need in front of them to decide it.
What changes on 1 January 2027
Section 25 of the Employment Rights Act 2025 cuts the qualifying period for ordinary unfair dismissal from two years to six months. The commencement date is set by SI 2026/559, and it is 1 January 2027. For the wider reform picture, see the two-year rule and why it is changing.
That is the mechanism behind everything else here. The latitude probation has always seemed to carry was never about the probation clause, it was about the qualifying period, and from 1 January 2027 that period runs out at six months' service instead of two years.
The compensatory award cap goes at the same time, and it is removed outright rather than raised. As at 6 April 2026 it stood at the lower of £123,543 or 52 weeks' gross pay. Read that alongside what tribunals actually award: Ministry of Justice data cited in the DBT factsheet records 646 unfair dismissal awards in 2023/24 at a median of £6,746. The ceiling is gone; the typical outcome is not transformed by that.
The Act also removes the power to vary the qualifying period by secondary legislation, so any future change to the six-month figure needs a new Act of Parliament.
Two smaller changes travel with it. The right to request written reasons for dismissal drops to six months' service, and the qualifying period for dismissal connected to a spent conviction is removed entirely under Schedule 3.
Now the correction, because this one is widespread. There is no day-one unfair dismissal right in the final Act, and there is no statutory initial period with a light-touch dismissal procedure. Both appeared in an earlier draft of the Bill and neither survived. From six months' service, the ordinary test applies in full: a fair reason plus a fair procedure. If your 2027 planning assumes a statutory lighter standard for new hires, it is built on an abandoned draft.
The scale is substantial. DBT analysis of the Labour Force Survey puts around 6.3 million employees, 22% of all employed people aged 16 and over, between six months' and two years' service with their current employer.
Re-timing probation and reviews before the deadline
Start with the transitional rule, because HR teams keep reading it backwards. The qualifying period is determined by the effective date of termination, not the hire date and not the date the process started. A termination with an EDT on or after 1 January 2027 falls under the six-month rule, whenever the employee joined.
For decisions being taken right now, that makes this a late-2026 operational issue rather than a 2027 project. Anyone whose six-month point or likely dismissal date straddles 1 January 2027 needs the EDT checked before the decision is finalised. Employees already past six months' service on 1 January 2027 become protected on that day.
Which brings us to the collision at the centre of this. The UK's most common probation length is six months. That used to sit safely inside a two-year window, and from January it lands exactly on the threshold. The government's stated rationale for choosing six months is that it gives employers time to assess new recruits, and that only holds if the probation process finishes before the clock runs out.
A five-step audit covers the ground:
- List current probation lengths by role, not just the headline figure in the standard contract.
- Check whether your contracts actually contain a written extension right.
- Map review dates against the six-month service point, with notice periods included in the arithmetic.
- Confirm that notice terms during and after probation are coherent with the new timetable.
- Brief line managers, because that is where probation processes actually fail.
One trap to separate out: shortening probation does not shorten contractual notice. Plenty of UK contracts set a shorter notice period during probation and a longer one after it, so a decision taken in good time at month three can still produce a termination date past six months if the notice provisions were not redesigned alongside the length. Design both together.
And one thing that needs no change at all. Discrimination and automatically unfair dismissal handling was always a day-one obligation. If those processes are weak, the reform has not caused the problem. It has only raised the price of it.
Where probation decisions still go wrong
Four failure patterns recur, and none of them are about length.
No written objectives, so the final review becomes a judgement about the person rather than a comparison against expectations that were set in advance.
Reviews held but never recorded, or recorded and never shared with the employee. Either way you reach the end with no evidence that the outcome was foreseeable, which is the first thing you need and the hardest thing to reconstruct afterwards.
Extensions confirmed verbally, or confirmed in writing after the original end date has passed. Acas warns that confirming an extension after the original end date could be a breach of contract.
Line managers treating probation as a period where ordinary fairness does not apply. That was never true, and after January 2027 it will be visibly untrue to anyone who reaches six months' service.
The teams that will find 2027 easiest are the ones whose probation process already produced a documented, unsurprising decision. The reform changes the timeline, not the standard.
Before the end of 2026, pull your current contract templates and check three things: the probation length attached to each role, whether a written extension right exists in the contract at all, and whether the final review plus the applicable notice lands before six months' service. If any of the three comes back unclear, that is the work.