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When probation ends, when to hold the review, and when unfair dismissal rights begin.
Written for employers. If you are an employee checking your own probation, the dates work the same way, but the rest of this page speaks to the employer.
Probation ends on
Give the start date and the length and the answer appears here. The calculation runs in your browser, and nothing you type is sent anywhere.
Until now probation sat well inside the two years it took to be able to claim ordinary unfair dismissal, so its length hardly mattered. From 1st January 2027 that qualifying period falls to six months, under section 25 of the Employment Rights Act 2025, brought into force for that date by the Employment Rights Act 2025 (Commencement No. 4 and Transitional and Saving Provisions) Regulations 2026. It applies wherever the employment ends on or after that day, whenever the person started.
Six months is a common probation length, and it now lands right on that date. Somebody who starts on 1st February 2027 on six months’ probation finishes it on 31st July 2027. The first day their employment could end with them able to claim unfair dismissal is 31st July 2027, the same day. A decision at the end of that probation is a decision about somebody with full unfair dismissal rights, and it needs a fair reason and a fair process like any other.
It is the end of the employment that counts, not the day you decide. Notice has to have run out first, and if you pay in lieu or end it without notice, the statutory week is added when the service is counted. The calculator gives you the last day a week’s notice still finishes in time.
More on both: unfair dismissal at six months, from January 2027, and can I dismiss someone during probation? The January 2027 employer checklist sets out the rest of what to check, item by item.
Probation is set by the contract, not by law, so the contract’s own wording comes first. Where it simply says “three months” or “twelve weeks”, the usual reading is a period that includes the first day and ends the day before the same date comes round again.
No law sets a date for it. The calculator suggests 14 days before the end, which leaves time to invite the employee, meet, decide and confirm the outcome in writing before the period has run out. Leave it until after the end date and, depending on how the contract is worded, the employee may already have passed.
Only where the contract allows it, and only before the first period ends. The extension runs from the day after the original end date, and the employee should have it in writing: why, what needs to improve, what support they will get, and the new end date. Put the new end date into the calculator and it will tell you whether the extension now runs past the point where unfair dismissal rights begin, which from 1st January 2027 it often will.
Short service is never protection against everything. A dismissal connected to pregnancy, whistleblowing, asserting a statutory right or a protected characteristic carries risk from the first day, and probation changes none of that. Nor does the calculator read your contract: if it defines the period differently, the contract wins.
See our disclaimer. This is a calculator rather than advice.
Tarn.hr walks you through a probation review: confirm, extend or end, with the invitation, the outcome letter and the dates, checked against UK employment law and the Acas codes.