Most employment contracts say "one calendar month's notice" without explaining how to calculate an actual end date from that. When a member of staff resigns, getting that date right is important as it affects final pay, holiday accrual, and when you can start recruiting.
Here is how UK notice periods work, and how to calculate the last day correctly.
- The notice period starts the day after notice is given, not the same day
- The last day is the same date next month as the date notice was given
- "One calendar month" and "four weeks" are not the same thing
- If that date doesn't exist in the next month, fall back to the last day of that month — and check the employee's contract
Check the contract first
The notice period is set by the employee's contract, not by a general rule. Most employers set a contractual notice period that is longer than the legal minimum.
The statutory baseline is one week's notice after a month of continuous employment, then one extra week per full year of service up to 12 weeks. Most office contracts require one or two months and sometimes three for senior roles. The contractual figure takes precedence. If the contract says nothing, the statutory baseline applies.
When does the notice period start?
Later than most people assume. According to ACAS guidance, the notice period starts the day after notice is given. If an employee resigns verbally on a Wednesday, Thursday is day one — not Wednesday.
The same rule applies when the employer gives notice of dismissal or redundancy.
Written notice adds a wrinkle: the clock starts from when the recipient could reasonably have read it, not when it was sent. A letter that arrives while an employee is on holiday will not start the period until they are back.
How to calculate the last day
The last day of employment is the same calendar date next month as the date notice was given and not the date the notice period started.
As an example, an employee hands in their notice on 15 January. The period starts on 16 January. The last day is 15 February, because the end date is tied to when notice was given, not when counting began.
| Notice given | Notice starts | Last day |
|---|---|---|
| 15 January | 16 January | 15 February |
| 1 March | 2 March | 1 April |
| 3 May | 4 May | 3 June |
| 30 November | 1 December | 30 December |
| 31 January * | 1 February | 28 February (non-leap) / 29 February (leap year) |
* When the corresponding date does not exist in the following month, the recommended approach is to use the last day of that month. Always check whether the employee's contract includes specific wording for this situation.
Calendar month vs four weeks
These are not interchangeable. Four weeks is always 28 days. A calendar month varies — January is 31 days, February is 28. If the contract says one calendar month, counting 28 days forward and stopping is wrong. Check the exact wording in the contract.
When the employer gives notice
The calculation is identical if it is the employer giving notice. A dismissal or redundancy letter handed over on 3 June, with one month's notice in the contract, means the last day is 3 July. If the notice is written, the clock starts when the employee could reasonably have read it, not from the postmark date.
Garden leave and PILON
Two ways a notice period gets served without the employee working it — and neither changes the end date.
Garden leave: the employee stays home but remains on the payroll, and employment ends on the same calculated date.
PILON (payment in lieu of notice): the employee leaves immediately and receives payment covering the notice period. They are gone sooner in practice, but the contractual end date is still the reference point for final pay and any outstanding leave.
You can only enforce PILON if the contract includes a PILON clause. Without one, the employee has to agree to it.
Frequently asked questions
Does a calendar month notice period include weekends and bank holidays?
Yes — weekends and bank holidays count. A calendar month runs through every day; you do not adjust for non-working days when calculating the last day.
Is one calendar month the same as four weeks' notice?
No. Four weeks is 28 days. A calendar month is 28, 29, 30, or 31 days depending on which month it falls in. In most months, one calendar month is longer than four weeks.
What happens if I hand in notice on the last day of the month?
If the corresponding date does not exist in the next month — for example, notice given on 31 January — the recommended approach is the last day of that month: 28 February in a standard year, 29 February in a leap year. Check your contract, as some include specific wording for this case.
Does the notice period start on the day the employee hands it in?
No. The notice period starts the day after notice is given. An employee who resigns on a Monday has Tuesday as day one of their notice period.
Can the notice end date be changed once notice has been given?
Not unilaterally by either side. The end date is set once valid notice is given. Any change needs both parties to agree, and it should be confirmed in writing.