What is a date difference calculator?
A date difference calculator tells you how much time separates two dates. It is useful for project timelines, notice periods, contract terms, visa stays, pregnancy and baby milestones, loan periods, and simply answering “how long ago was that?”. Counting on a calendar is slow and easy to get wrong when the range crosses months of different lengths or a leap year; the calculator does it instantly and precisely.
Alongside the total number of days, it shows the same span as calendar years, months and days, as weeks plus leftover days, as hours, and as working days from Monday to Friday.
How to use it
- Choose the start date and the end date.
- Tick include the end date if both the first and last day should count, for example when counting days of leave or the length of an event.
- Read the total days and the breakdowns. If the end date is earlier than the start, the calculator shows the gap between them.
How the counting works
By default the calculator counts the number of midnights between the two dates, which is how durations are normally measured: from Monday to Tuesday is one day. Including the end date adds one day, which is how people usually count attendance, hotel nights plus checkout days, or annual leave.
Working days count every Monday to Friday in the range. Public holidays differ between countries and regions, so they are not removed automatically; subtract them yourself if they apply.
Examples
- 1 January to 31 December 2026 is 364 days (52 weeks), or 365 days when you include the end date.
- The whole of 2026 contains 261 working days from Monday to Friday.
- 31 January to 1 March 2000 (a leap year) is 30 days, or 1 month and 1 day.
More worked examples
Leap year: 1 Jan 2024 to 1 Jan 2025 is 366 days because 2024 had 29 February.
Notice period: 6 Oct 2026 to 3 Nov 2026 is 28 days, or exactly 4 weeks.
Common mistakes to avoid
- Forgetting to include the end date. For leave or event days, tick “include the end date”.
- Assuming every month has 30 days. Months vary from 28 to 31 days, which matters for contracts.
- Counting public holidays as working days. Holidays differ by country, so subtract them yourself. To count down to a single date, use the days until calculator.
Sources and methodology
The calculations on this page follow these published standards and references. The code is covered by automated tests against known values.
- Gregorian calendar leap-year rule (years divisible by 4, except centuries not divisible by 400)
- ISO 8601 – Date and time format