Date Calculator
Add or subtract years, months, weeks, and days from a starting date. The result includes a calendar date and weekday, with month-end clamping so an offset never creates an impossible date.
Date Calculator tool
About the Date Calculator
Use this tool for tentative schedules, anniversary planning, and calendar checks. Choose addition or subtraction and enter whole, nonnegative amounts for each unit.
How Is Date Calculated?
Years and months are combined into a single calendar-month offset. The starting day is clamped to the destination month's last day if necessary. Weeks and days are applied afterward as calendar-day offsets.
Calendar-month offset = 12 × years + months
Calendar-day offset = 7 × weeks + days
Result = clamped month-shifted start date ± calendar-day offset
Example
January 31, 2024, plus 1 month and 1 day becomes February 29 after clamping, then March 1 after adding the day.
How to Use the Date Calculator
- Enter a valid starting date.
- Select Add or Subtract.
- Enter whole numbers for years, months, weeks, and days, leaving unused units at zero.
- Read the resulting date and weekday.
- Review the order of operations when working near a month end.
Date Calculator Examples
Non-leap February
January 31, 2023, plus 1 month is February 28, 2023, a Tuesday.
Subtracting a month
March 31, 2024, minus 1 month is February 29, 2024, a Thursday.
Weeks and days
March 9, 2024, plus 1 week and 1 day is March 17, 2024, a Sunday.
Calendar months are not fixed durations
One month is not always 30 days and one year is not always 365 days. Use days or weeks when you need a fixed number of calendar days.
Planning limitations
Dates are processed in UTC to avoid local timezone and daylight-saving changes. This tool does not calculate clock times.
Official filing and payment deadlines may use special rules for holidays, weekends, and inclusive counting. Confirm those rules separately.
Frequently Asked Questions
What happens when a month does not have the starting day?
The date is clamped to that month's last day. January 31 plus one month is February 28 or 29.
In what order are offsets applied?
Years and months are combined and applied first with one clamping step. Weeks and days are then combined and applied.
Is subtracting an offset always the inverse of adding it?
No. Clamping can discard the original day. January 31 plus one month and then minus one month may return January 28 or 29.
Can I enter negative amounts?
Use the Subtract mode instead. Each amount must be a nonnegative whole number no greater than 1,000,000, and the result must stay within years 0001 through 9999.
Are holidays and weekends skipped?
No. Every day is a calendar day. The weekday is displayed, but no business-day or holiday adjustments are made.