Add or Subtract from a Date
The Add/Subtract panel lets you find what date falls a certain number of days, weeks, months, or years before or after a start date. All four fields are additive: if you enter 1 year and 6 months, the result is 18 months from your start date. Days and weeks are combined and added first, then months, then years, matching standard calendar arithmetic.
Date Difference
The Date Difference panel calculates the gap between two dates. Total days is exact. Total weeks divides total days by 7. Total months and total years are approximations based on average days per month (30.4375) and average days per year (365.25).
Frequently Asked Questions
Select the 'Add/Subtract from Date' tab, enter your start date, choose 'Add' or 'Subtract', then enter the number of days, weeks, months, or years. The result date updates instantly.
Select the 'Date Difference' tab, enter a start date and an end date, and the calculator shows the difference in years, months, days, total days, total weeks, and total months.
Yes. Adding or subtracting days uses JavaScript's built-in date arithmetic, which correctly handles leap years, month-end differences, and daylight saving transitions.
Adding one month to January 31 produces February 28 (or February 29 in a leap year), since February does not have 31 days. This is the standard behavior for calendar month arithmetic: the result is clamped to the last valid day of the target month.
This calculator counts all calendar days, not just business days. Business day calculation depends on regional holidays which vary by country and state, so it is not included here.
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