makeatimerDates
Date difference calculator
Find the number of calendar days, months, and years between two dates.
Dates
Add or subtract dates
Move a calendar date forward or back by days, months, and years.
Inputs
Result
Saturday · month-end dates are clamped to the last valid day
How to use add or subtract dates
Find a date after a project interval or work backwards from a milestone. Calendar months keep the day number when possible and use the last valid day when necessary.
Worked example
January 31, 2026 plus one month becomes February 28, 2026. January 31, 2024 plus one month becomes February 29.
What the result means
Years and months are applied together, then days. Month-end clamping is explicit; adding and subtracting a month may not return the original date.
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