Date Calculator
Find the difference between two dates or add and subtract days from any date.
Choose a mode at the top. Difference mode asks for a start and end date and reports the gap in total days, weeks plus remaining days, and approximate months. Add-subtract mode asks for a start date and a number of days to add or remove.
All date math is done at the UTC midnight boundary, so crossing daylight saving time boundaries or time zones does not shift the result by an hour. Enter dates in the standard year-month-day format.
Use the difference mode for deadlines, age-related day counts, and project durations. Use the add-subtract mode to find what date falls a certain number of days before or after another date.
Frequently asked questions
How is the day count calculated?
Both dates are converted to UTC midnight timestamps. The difference in milliseconds is divided by the exact number of milliseconds in a UTC day, giving a whole-day count without DST shifts.
What does approximate months mean?
Approximate months is the day difference divided by 30.44, which is the average length of a calendar month. It is a rough estimate, not a calendar-month boundary calculation.
Can I calculate a date in the past?
Yes. In add-subtract mode, enter a negative number of days to go backward from the start date. The result updates immediately.