Date Add & Subtract Calculator
Calendar date arithmetic
Add to or subtract from a date
Result
Calculation summary
Enter values to see the result
Date transformation
Base date to result date
How to use this calculator
- 1Choose a base calendar date and select add or subtract.
- 2Enter any combination of whole years, months, weeks, and days.
- 3Calculate to see the resulting date, weekday, and net calendar-day shift.
Formula
Result = base date ± years ± months ± weeks ± days
Components are applied in that fixed order. Calendar years and months clamp to a valid month end before fixed seven-day weeks and calendar days are applied.
Calculation steps
- Validate the base date and nonnegative whole-number amounts.
- Apply signed calendar years, clamping an unavailable anniversary.
- Apply signed calendar months, clamping an unavailable day of month.
- Apply weeks as seven calendar days, then apply remaining days.
- Verify the result remains between years 0001 and 9999.
Worked example
Adding one month to January 31, 2026 returns February 28, 2026 because February 31 does not exist. A visible month-end adjustment note is included.
Assumptions
- Date components are applied in years-months-weeks-days order; changing the order can produce a different result.
- An unavailable day is clamped to the last valid day of the target month.
- Weeks always equal seven calendar days.
- The calculation uses Gregorian date-only values without a time or time zone.
- The supported output range is year 0001 through 9999.
Sources
Frequently asked questions
What is one month after January 31?
Under this calculator’s explicit clamp policy, it is the last valid day of February.
Does one year always equal 365 days?
No. Years are calendar components and can cross a leap day. The result also shows the actual net calendar-day shift.
In what order are amounts applied?
Years, then months, then weeks, then days. The order is fixed and shown in the result assumptions.
Can I enter negative values?
Use the subtract operation and enter nonnegative whole amounts. This keeps share URLs and the displayed operation unambiguous.
Does this use business days?
No. Weeks and days are calendar units. Use the business days calculator when weekends and custom holidays must be excluded.