Date Difference Calculator
Calculate the exact number of days, weeks, months and working days between two dates, with leap years handled correctly.
Last reviewed by the Radiatus Cloud team
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The first question any date difference raises is whether both endpoints count. From 1 March to 3 March is two days if you count the gap and three if you count the days involved. Contracts, notice periods and hire durations differ on this, and the convention is rarely stated. Decide which you need before trusting any figure: an off-by-one here has ended up in court more than once.
Months are not a fixed unit
A difference in months is ambiguous whenever the day-of-month does not exist in the target. What is one month after 31 January? Different systems answer 28 February, 2 March or 3 March. The common convention, used here, clamps to the last valid day of the target month, so 31 January plus one month is 28 February. Expressing long spans in days avoids the ambiguity entirely.
Working days need a definition
Excluding weekends is straightforward. Public holidays are not: they vary by country, by region within a country, and by year, and some move with Easter. A working-day count is only as good as the holiday list behind it. For anything contractual, confirm which calendar applies rather than assuming the default.
Leap years and the 400-year rule
Every year divisible by 4 is a leap year, except centuries, except centuries divisible by 400. So 1900 was not a leap year and 2000 was. Spreadsheets have historically shipped with a deliberate bug treating 1900 as a leap year, retained for backward compatibility, which makes date arithmetic spanning that year off by one in some tools.
Time zones make a day ambiguous
Two timestamps can fall on different calendar dates depending on the zone used to render them, so a difference in days can vary by one. Where a date difference matters legally or financially, fix the time zone explicitly rather than relying on the viewer's local setting.
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Frequently Asked Questions
Should both dates be included in the count?
It depends what you are measuring, and the convention is rarely stated. From 1 to 3 March is two days as a gap and three as days involved. Contracts and notice periods differ; decide before trusting a figure.
How are months counted between dates?
By clamping to the last valid day where the day-of-month does not exist, so 31 January plus one month is 28 February. Different systems answer differently, so express long spans in days when precision matters.
How are working days calculated?
Weekends are straightforward; public holidays are not. They vary by country, by region and by year, and some move with Easter. A working-day count is only as reliable as the holiday calendar behind it.
Which years are leap years?
Those divisible by 4, except centuries, except centuries divisible by 400. So 1900 was not and 2000 was. Some spreadsheets retain a deliberate 1900 bug for compatibility, which skews arithmetic spanning that year.
Can time zones change the result?
Yes. Two timestamps can fall on different calendar dates depending on the zone used to render them, so a day count can differ by one. Fix the zone explicitly where the result matters legally or financially.
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Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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