Date Calculator
Add/subtract time from a date, or find the difference between two dates.
🔒 Runs entirely in your browser — nothing is uploaded.
Result:
How Date Calculator works
How does the date calculator handle its two modes?
In add/subtract mode, it takes a start date and shifts it by a number of days, weeks, months, or years using the browser's native date arithmetic. In difference mode, it compares two dates with the same calendar-aware logic as the age calculator, breaking the gap into years, months, and days rather than just a day count, plus showing the raw total days separately.
When would I use add/subtract versus the difference mode?
Add/subtract is for forward planning, like finding the date 90 days from a contract signing or 6 weeks before a deadline. Difference mode is for looking backward at two known dates, such as figuring out exactly how many years, months, and days apart two events fell.
What happens if I add a month to a date like January 31st?
Because month and year shifts rely on the browser's native date rollover behavior, adding one month to January 31 doesn't land on a nonexistent "February 31" — it overflows into early March instead, since February has fewer days. This is standard JavaScript date-math behavior rather than a bug, but it's worth double-checking results for month-end dates where the target month is shorter.