How to calculate the days between two dates
Learn how date differences work, when to count the start or end date, and why calendar days differ from working days.
Start with the dates
Identify the earlier and later calendar dates. A date difference measures elapsed days between them; it does not automatically count both endpoints.
Worked example
From 10 October to 17 October there are 7 elapsed days. If a rule counts both 10 and 17 October inclusively, the count is 8 calendar dates instead.
Calendar days versus working days
Calendar days include weekends. Working days depend on the workweek and any excluded holidays. For deadlines, check which convention applies before using the result.
Leap years and months
Do not assume every month has 30 days or every year has 365 days. February can have 29 days in a leap year, so use real dates rather than a fixed multiplication.
Try it yourself
Enter two dates in the date difference calculator, then compare the result with the working days calculator when weekends or holidays matter.