Date Calculator
Choose a calculation type below. Results update automatically as you change the dates.
Full Breakdown
Date Calculator UK
Our Date Calculator combines two tools in one: an add/subtract calculator that finds a new date after adding or removing days, weeks, months or years, and a date difference calculator that works out exactly how much time falls between two dates — including a full weekday and weekend breakdown.
How to Use the Date Calculator
- Choose a calculation type using the buttons at the top: “Add/Subtract From A Date” or “Difference Between Two Dates”.
- For add/subtract: enter a start date, an amount, choose a unit (days, weeks, months or years), and choose whether to add or subtract. Quick presets are available for common amounts.
- For date difference: enter Date A and Date B in either order — the calculator automatically works out which one is earlier.
- Results update automatically as you change the dates, or click Calculate to refresh manually.
- Use Copy Results to copy a plain-text summary, or Print for a printable version.
Adding or Subtracting Months and Years
Adding months or years to a date isn’t as simple as adding a fixed number of days, because calendar months have different lengths. This calculator handles that correctly: if adding a month would land on a day that doesn’t exist in the target month — for example, adding one month to 31 January — the result is clamped to the last valid day of that month (28 or 29 February), rather than rolling over into March.
| Calculation | Result |
|---|---|
| 31 January + 1 month | 28 February (29 February in a leap year) |
| 15 March + 90 days | 13 June |
| 1 January 2024 + 1 year | 1 January 2025 |
| 29 February 2024 + 1 year | 28 February 2025 (2025 is not a leap year) |
How the Date Difference Calculator Works
The date difference calculator counts every calendar day between your two dates and classifies each one as either a weekday (Monday to Friday) or a weekend day (Saturday or Sunday). It also gives you the total in weeks, and an exact years/months/days breakdown, so you can see the gap between two dates however suits you best — useful for working out project timelines, notice periods, contract lengths, or time until an event.
Common Uses for a Date Calculator
- Deadlines and notice periods: Add a set number of days to a start date to find a deadline, or check how many working days remain.
- Contract and project lengths: Find the exact duration between a start and end date, including a weekday count for billing or scheduling.
- Age or anniversary milestones: Add years to a date to find a future anniversary, or use our Age Calculator for exact age from a date of birth.
- Travel and event planning: Count down the days to a trip or event, or work out arrival/return dates from a given length of stay.
Important Assumptions
- Calculations use calendar dates only, so results are accurate to the nearest day.
- Adding months or years clamps the result to the last valid day of the target month where necessary (see the table above).
- The “difference between two dates” calculation works regardless of which date is entered first.
- Weekday/weekend breakdowns use the standard UK convention of Saturday and Sunday as the weekend.
- ISO week numbers follow the ISO 8601 standard, where week 1 contains the year’s first Thursday.
Frequently Asked Questions
How do I add or subtract days from a date?
Enter a start date, an amount, and choose a unit (days, weeks, months or years) and a direction (add or subtract). The calculator gives you the resulting date along with the day of the week.
How is the difference between two dates calculated?
The calculator counts the number of calendar days between the two dates you enter, and also breaks this down into years, months and days, total weeks, and the number of weekdays and weekend days in between.
What happens if I add a month to the end of a month, like 31 January?
Adding a month to 31 January gives 28 February, or 29 February in a leap year, since February does not have 31 days. The calculator clamps the result to the last valid day of the target month rather than overflowing into March.
Does the date difference count weekends?
Yes. The difference calculator shows the total number of days between two dates, and separately breaks that total down into weekdays (Monday to Friday) and weekend days (Saturday and Sunday).
Does it matter which date I enter first?
No. If Date A is after Date B, the calculator automatically works out which date is earlier and calculates the difference correctly, noting this in the summary.
What is an ISO week number?
An ISO week number identifies which week of the year a date falls in, using the ISO 8601 standard where week 1 is the week containing the year’s first Thursday and weeks run Monday to Sunday.