Date Calculator
The Date Calculator calculates exact, real-time domain outputs in active voice. The Date Calculator adds or subtracts any combination of years, months, weeks, and days from a starting date to determine the exact future or past calendar date, day of the week, and ISO week number.
Interactive Date Calculator Workspace
Launch Interactive Date Calculator →
Date Calculator Input Parameters & Defaults
| Start Date (YYYY-MM-DD) | 2026-11-06 | Starting calendar date. |
| Operation (1 = Add +, -1 = Subtract -) | 1 | 1 to Add duration, -1 to Subtract duration. |
| Years | Years to add/subtract. | |
| Months | 3 | Months to add/subtract. |
| Weeks | 2 | Weeks to add/subtract. |
| Days | 10 | Days to add/subtract. |
Date Calculator Mathematical Formula
D_{\text{target}} = D_{\text{start}} \pm (\Delta Y \text{ yrs} + \Delta M \text{ mos} + 7\Delta W \text{ days} + \Delta d \text{ days})Date Calculator Worked Example
Adding 1 year, 3 months, 2 weeks, and 10 days to 2026-11-06.
- Add 1 year and 3 months to 2026-11-06 -> 2028-02-06.
- Add 2 weeks (14 days) + 10 days = 24 days -> 2028-03-01 (2028 is a leap year with 29 days in February).
Because 2028 is a leap year, February has 29 days, placing the final date on March 1, 2028.
Date Calculator Glossary of Key Terms
Start Date (YYYY-MM-DD) (Date Calculator)
Starting calendar date.
Operation (1 = Add +, -1 = Subtract -) (Date Calculator)
1 to Add duration, -1 to Subtract duration.
Years (Date Calculator)
Years to add/subtract.
Months (Date Calculator)
Months to add/subtract.
Gregorian Leap-Year Rule
The calendar rule stating that a year is a 366-day leap year if divisible by 4, excluding century years not divisible by 400.
ISO-8601 Week Date
An international standard where weeks start on Monday and Week 1 contains the year's first Thursday.
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Date Calculator Frequently Asked Questions
Q: How do 90-day notice periods or visa stays compare to 3 calendar months?
Three calendar months can equal 89, 90, 91, or 92 days depending on which months are crossed. Legal contracts specifying '90 days' count exact 24-hour calendar days rather than month numbers.