Date Calculator
Pick a start date, choose add or subtract, then enter any mix of years, months, weeks and days. The answer updates as you type.
Years and months are applied first, then weeks and days. If the day does not exist in the new month, the answer is the last day of that month.
Worked examples
Month end
31 January 2026, add 1 month
Saturday 28 February 2026
There is no 31 February, so the last day of February is used.
Leap year
31 January 2028, add 1 month
Tuesday 29 February 2028
2028 is a leap year, so February has 29 days.
Mixed period
18 October 2026, add 1 year, 2 months, 3 weeks and 4 days
Wednesday 12 January 2028
One year and two months reach 18 December 2027, then 25 days more.
About Date Calculator
A date calculator finds the date that is a set amount of time before or after another date. You might want the end of a 90 day notice period, the date six months after a contract starts, the day a warranty of two years and three months runs out, or the date eight weeks before an event. Pick the start date, choose add or subtract, and type any mix of years, months, weeks and days. The result appears at once with its day of the week, so you can see straight away if it lands on a weekend.
Months are the awkward part, because they have different lengths. Adding one month to 31 January cannot give 31 February, so the answer is the last day of the shorter month: 28 February, or 29 in a leap year. Subtracting one month from 31 March works the same way. This calculator applies years and months first, then weeks and days, and tells you whenever it has used the month end rule so that you can check it against the wording in your contract or notice.
How to use Date Calculator
- Choose a start date with the date picker.
- Select whether to add to the date or subtract from it.
- Type the number of years, months, weeks and days. Leave any box at zero if you do not need it.
- Read the new date, its weekday, the number of calendar days between the two dates and the week number.
Common uses
- Working out the end of a notice period, probation or trial
- Finding a deadline eight or twelve weeks before an event
- Planning when a warranty, licence or subscription ends
- Checking a date six months or a year ahead for a review
Frequently asked questions
What happens when I add a month to the 31st?
If the new month is shorter, the answer is the last day of that month. 31 January plus one month is 28 February in 2026 and 29 February in 2028. Taking one month from 31 March also gives the end of February.
Are years and months applied before days?
Yes. Years and months are added first, with the month end rule if needed, and then weeks and days are counted one calendar day at a time. This order matches how most people read a period such as one month and ten days.
Do clock changes or leap years affect the answer?
No. The calculation uses calendar dates only, with no times of day, so the clocks going forward or back cannot move the result. Leap days are counted when they fall inside the period.
Does it count weekends and bank holidays?
Yes, every calendar day counts. If you need to skip weekends and bank holidays, use the working days calculator instead.
Can I use it for legal deadlines?
It gives the arithmetic, but courts, contracts and public bodies sometimes count periods differently, for example by excluding the first day. Check the exact wording of the rule that applies to you.