Date Add/Subtract Calculator
Add or subtract years, months, weeks, and days from a date
Date Manipulation
Add or subtract time periods
Multiple Units
Years, months, weeks, and days
Frequently asked questions
What happens if adding months lands on a day that doesn't exist in the target month, like January 31st plus one month?
The calculator uses JavaScript's native date rollover rather than clamping to the month's last day, so January 31st plus one month spills over into March instead of landing on February 28th, since February doesn't have 31 days.
Why do I have to enter positive numbers even when I choose "Subtract"?
The years, months, weeks, and days fields only accept non-negative values. The Add/Subtract toggle controls direction internally by negating each value before applying it, so you always type a positive amount of time regardless of which way you're moving the date.
In what order are years, months, weeks, and days applied?
Years are applied to the date first, then months, then weeks and days are combined into a single day offset and applied last. It's a sequence of adjustments to the same date rather than one simultaneous shift, which can matter when a month change affects how a later day offset lands.
Can I calculate a result without entering any time amount?
No. The Calculate button stays disabled until a start date is set and at least one of years, months, weeks, or days is greater than zero.