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Date Calculator

Find the exact difference between two dates, or add and subtract years, months, weeks and days from a date. It handles month lengths and leap years for you.

How it works Report a problem

Date Engine Pro

Dynamic intervals, holidays, and time projection

Total Difference
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0
Years
0
Months
0
Weeks
0
Days

Detailed Insights

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About the Date Calculator

Find the exact difference between two dates, or add and subtract years, months, weeks and days from a date. It handles month lengths and leap years for you.

How to use the Date Calculator

  1. To find a difference, enter a Starting Point and an Ending Point, then press Calculate Difference.
  2. To add or subtract time, enter a Starting Date, choose Go Forward in Time (+) or Go Backward in Time (−), and enter the Years, Months, Weeks and Days, then press Add or Subtract Time.

Formula and method

The calculator uses the Gregorian calendar. Adding months moves to the same day of a later month (adjusted to the last day if the month is shorter), and leap years add 29 February.

Worked example

Adding 3 months and 10 days to 15 January 2026 gives 25 April 2026. The difference between 1 January 2026 and 1 March 2026 is 59 days.

When to use the Date Calculator

  • Finding the date that is a certain number of days, weeks or months away.
  • Working out deadlines, due dates and contract end dates.
  • Checking how long ago or how far ahead an event is.

Common mistakes to avoid

  • Assuming every month has 30 days when counting forward.
  • Forgetting whether the start day is included in the count.
  • Ignoring leap years when counting across several years.

Tips

  • Use it for contract deadlines, project schedules, notice periods and pregnancy or warranty dates.
  • Business-day calculations exclude weekends and holidays and need a separate calculator.

Frequently asked questions

How do I find the date 90 days from today?
Enter today as the starting date, choose Go Forward, and enter 90 in the Days box.
Does the calculation include the start date?
Usually the start date is not counted. Check the option in the tool if you need it included.
How are months added?
By calendar month. Adding one month to 31 January gives the last day of February.