Date Calculator
Calculate the difference between dates, add or subtract time periods, and find business days, weekends, and more.
Business Days
Weekdays count excludes weekends (Saturdays and Sundays). Useful for project planning.
Leap Years
Leap years occur every 4 years, except for years divisible by 100 but not by 400.
About the Date Calculator
This date calculator adds and subtracts days, weeks, months and years from a date, finds the interval between two dates, and identifies weekdays — handling leap years and month lengths from the real calendar.
A date calculator answers both directions of the same question: what date is 90 days from now, and how many days are there until a given date. Contract terms, notice periods, invoice due dates and project deadlines all reduce to one or the other.
Adding months is less obvious than it looks. One month after 31 January cannot be 31 February, so it has to resolve to 28 or 29 depending on the year — and different systems resolve it differently. That ambiguity is why month arithmetic causes so many off-by-one billing errors.
Weekday identification matters for anything commercial, since a deadline that lands on a Saturday usually moves. Leap years are handled from the actual calendar rather than approximated, so a span crossing 29 February counts correctly.
How to use the Date Calculator
- Pick a mode. Add or subtract from a date, or find the interval between two.
- Enter the date. Provide the starting date.
- Set the amount. Enter the days, weeks, months or years to apply.
- Read the result. See the resulting date and which day of the week it falls on.
Date Calculator features
- Add or subtract days, weeks, months and years
- Interval calculation between two dates
- Weekday and weekend identification
- Leap years handled from the real calendar
- Sensible month-end resolution
- Runs entirely in your browser
Frequently asked questions
What happens when I add a month to 31 January?
It resolves to the last day of February, since 31 February does not exist. That ambiguity causes many billing off-by-one errors.
Does it show the day of the week?
Yes, which matters for commercial deadlines that move when they land on a weekend.
Are leap years handled?
Yes, from the actual calendar rather than by approximating a year as 365 days.
Can I calculate backwards?
Yes. Subtracting works the same way as adding, for notice periods and retrospective dates.
Is my input uploaded?
No. Everything is calculated in your browser.