Date Calculator
Pick a start date, choose add or subtract, and enter a duration.
Calculation
Result date:
Month addition uses calendar months from the start day (same day-of-month when possible).
Why "months" is labeled approximate
Adding or subtracting days and weeks is exact, since those units have a fixed, unchanging length. Months don't — they range from 28 to 31 days — so adding "1 month" to January 31st, for example, rolls over to a valid date in the following month using JavaScript's calendar-aware date math, which can shift the day-of-month when the target month is shorter (e.g., adding a month to January 31 can land on March 3 rather than a nonexistent February 31).
Frequently asked questions
Why would adding a month not land on the same day-of-month? If the starting day doesn't exist in the target month (like the 31st added to a 30-day month), the date automatically rolls forward into the next month — this is standard calendar arithmetic behavior, not a bug.
Can I use this to count down to a deadline? Yes — set your deadline as the start date and use "subtract" with today's implied context, or more simply, calculate forward from today by the number of days/weeks until your target date to double-check a due date.
Does this account for time zones? The calculation is done using local calendar dates (noon local time is used internally to avoid daylight-saving edge cases), so results are consistent for whichever date you select regardless of your device's time zone.