How to use the date difference calculator
- Choose “Days between dates” or “Add or subtract”.
- Enter the start and end dates, and choose whether to include the end date in the count.
- Optionally list public holidays that apply to you so they are excluded from business days.
- To add or subtract, enter a start date, an amount and a unit such as calendar days or business days.
Worked example
25 September 2026 to 25 December 2026
There are 91 days between the dates (end date not included), which is exactly 13 weeks or 3 months, and 65 business days. Adding 10 business days to Friday 25 September 2026 gives Friday 9 October 2026.
How it works
Dates are converted to whole UTC day numbers, so the difference is exact and unaffected by daylight saving changes. Years, months and days use calendar months with month-end clamping. Business days count Monday to Friday in the same span as the calendar days, minus any holiday dates you list that fall on weekdays. Adding business days steps one day at a time, skipping weekends and your holidays.
Assumptions
- Weekends are Saturday and Sunday.
- No public holidays are assumed; enter your own.
- With “include end date” off, the span includes the start date and excludes the end date.
Frequently asked questions
Should I include the end date?
Include it when you count both the first and last day, for example the length of a leave period from Monday to Friday (5 days). Leave it off for elapsed time, for example days until an event.
Why do I have to enter holidays myself?
Public holidays differ by country, state and employer. Paste the dates that apply to you, one per line or separated by commas.
What happens when adding a month to 31 January?
The result is the last day of February (28 or 29), because 31 February does not exist.
Limitations
- Only Saturday and Sunday weekends are supported.
- Dates must be between years 1 and 9999.