Date Calculator
Add or subtract days from a date.
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What this date calculator does
Add or subtract days from a calendar date and determine the resulting date.
How to use the calculator
Enter the starting date and the number of days to add or subtract. This is useful for deadlines, planning, due dates and date intervals.
How the calculation works
The calculator performs calendar arithmetic while accounting for month lengths and leap years. It does not assume every month has the same number of days.
What the result means
Example: adding 30 days to January 1 produces January 31. Negative days move the result backward.
Important assumptions and limitations
If a contract or law defines a deadline using business days, calendar days or a specific counting convention, follow that rule rather than relying on a general date calculation.
Frequently asked questions
Can I add negative days?
Yes. A negative number subtracts days from the start date instead of adding them.
Yes. A negative number subtracts days from the start date instead of adding them.
Does it account for leap years?
Yes. The calculation uses calendar-date arithmetic, so February 29 is handled when it occurs.
Yes. The calculation uses calendar-date arithmetic, so February 29 is handled when it occurs.
Does it count the start date as day zero?
Yes. Adding 1 day to January 1 produces January 2; the starting date itself is not counted as an added day.
Yes. Adding 1 day to January 1 produces January 2; the starting date itself is not counted as an added day.
Can I use dates across different years?
Yes. The calculator can move forward or backward across months, years and leap years.
Yes. The calculator can move forward or backward across months, years and leap years.
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