Add/Subtract Date Calculator
Add or subtract days, weeks, months and years from any date. Select a starting date, enter a time period and instantly calculate the resulting future or past date.
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How to Use the Add/Subtract Date Calculator
- Select a date in the Starting Date field.
- Choose Add Time to calculate a future date or Subtract Time to calculate a past date.
- Enter the number of years, months, weeks or days.
- Keep the month-end adjustment option checked to automatically correct invalid dates.
- Click Calculate New Date.
- Review the calculated date, weekday, original date and total calendar-day difference.
- Click Use Today to select the current date.
- Click Reset to clear the entered values and start again.
How Does the Add/Subtract Date Calculator Work?
Years and months are combined into one month change: years x 12 + months. That change is applied first, then weeks x 7 + days is applied as a calendar-day change. Add Time makes both changes positive; Subtract Time makes both negative. The sequence matters near a month end.
One week is treated as seven calendar days. Calendar days include weekdays, weekends and public holidays.
Month lengths are handled automatically. For example, adding one month to January 15 produces February 15.
Some dates do not exist in the following month. If month-end adjustment is enabled, adding one month to January 31 produces the final valid day of February.
The calculated result also shows the weekday and the actual number of calendar days between the starting date and the resulting date.
Month lengths and leap years are included, but a calendar month is not a fixed number of days. Total Calendar Days shows the absolute date gap; Operation identifies whether time was added or subtracted.
Verified Date-Shifting Examples
With month-end adjustment on, January 31, 2025 plus 1 month gives February 28, 2025, a gap of 28 days. January 31, 2024 plus 1 month gives February 29, 2024, a gap of 29 days.
With adjustment off, January 31, 2025 plus 1 month gives March 3, 2025. The attempted February 31 overflows by three days into March. Keep adjustment on when you want the last valid day of a shorter target month.
Mixed units: January 31, 2025 plus 1 month and 1 day, with adjustment on, first becomes February 28 and then March 1, 2025. The total gap is 29 calendar days. Applying the day first would be a different sequence.
Subtract example: March 1, 2026 minus 2 weeks gives February 15, 2026, a gap of 14 calendar days. Leap-day example: February 29, 2024 plus 1 year, with adjustment on, gives February 28, 2025, a gap of 365 days.
Input and Calendar Limits
Use whole, non-negative amounts and choose Subtract Time to move backward. Negative or fractional amounts are not accepted; blank amounts mean zero. The resulting year must stay between 1 and 9999.
These are Gregorian calendar shifts, not business-day or elapsed-hour calculations. Weekends and holidays are not skipped, and no time zone or clock time is applied. A separate deadline-counting rule may differ from a simple calendar shift.
Frequently Asked Questions
How do I subtract time from a date?
Select the starting date, choose Subtract Time, enter the number of years, months, weeks or days and click Calculate New Date.
Can I add years, months, weeks and days together?
Yes. You can enter values in multiple fields at the same time. The calculator applies the years and months first, followed by the weeks and days.
What happens when the resulting month has fewer days?
When month-end adjustment is enabled, the calculator moves the result to the final valid day of the target month. For example, one month after January 31 may become February 28 or February 29.
What does the month-end adjustment option do?
When checked, the target month is limited to its last valid day: January 31, 2025 plus 1 month becomes February 28. When unchecked, surplus days carry into the next month, giving March 3 in that example. Weeks and days are applied after this month step.
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