About this tool
Counting days between dates by hand is error-prone: months vary from 28 to 31 days and leap years add 29 February. This calculator handles those boundaries and returns the gap in several units at once.
The second panel works the other way: start from a date and add or subtract a number of days, weeks, months or years to find a deadline, due date or notice period end.
How to use the Date Difference Calculator
- Choose a start date and an end date. If they are in the wrong order the tool swaps them.
- Tick "Include the end date" if both days should be counted, for example for a hotel stay or leave period.
- Press Calculate difference to see days, weeks, months, years and weekdays.
- To find a future or past date, use the second panel: pick the operation, an amount and a unit.
Practical examples
How it works
The day count is the difference of two UTC midnight timestamps divided by 86,400,000 milliseconds, which avoids daylight-saving errors. Including the end date adds one.
Years, months and days use calendar subtraction with borrowing from the real previous-month length. Approximate months and years use 30.4375 and 365.25 days.
Adding months or years keeps the same day of month, and clamps to the last valid day when needed (31 January + 1 month = 28 or 29 February).
Weekdays counts Monday to Friday only; it ignores public holidays.
Privacy and file processing
Dates are processed locally.
See our Privacy Policy for details on cookies, local storage and advertising.
Frequently asked questions
Does the count include the end date?
Not by default. Tick the checkbox if you want both ends counted.
Are leap years handled?
Yes, including century rules such as 2100 not being a leap year.
Can it skip public holidays?
No. Holidays differ by country and region, so only Monday to Friday weekdays are counted.
How far back can I go?
Any valid date from year 1 to 9999.
Related tools
Results are for general information. Check important figures against official sources. Read the disclaimer.