Date Calculator — Add or Subtract Days from a Date
Pick a start date, choose to add or subtract days, and instantly find the resulting date — with the day of the week, week count and a timeline overview.
開始日期
運算
天
此計算機如何運作？
Result date = Start date + N days (or − N days). Enter a date and a day count; the calculator shifts the date by the exact number of days using real timestamps — leap years and month lengths are handled automatically. The day of week, week count and a timeline are shown for the result.
公式
How this is calculated
The calculator adds or subtracts a whole number of days directly to the timestamp of the start date, anchored at midnight (00:00). Because it works on real timestamps, leap years (including February 29) and month-length differences (28-31 days per month) are handled automatically — no 30-day-month approximation is used for the result date itself.
The result is displayed in human-readable form (day of week, month name, year) as well as in ISO 8601 format (YYYY-MM-DD) for use in spreadsheets or code. The timeline bar shows the direction and span of the shift at a glance.
Approximate months are calculated by dividing the total days by 30.4375 (the average Gregorian calendar month, 365.25 ÷ 12). This is only an approximation — the exact calendar months depend on which specific months are crossed. For precise month arithmetic, see the date-difference calculator, which walks month-by-month.
常見問題
Leave the start date as today, choose "Add days" and enter 30. The result date changes as the number of days changes, taking leap years and different month lengths into account automatically.
Yes. The calculation is based on actual timestamps, so February 29 is counted correctly when the span crosses a leap year.
The day of the week is read directly from the result Date object using JavaScript's standard calendar, so it is always correct regardless of how many days were added.
也稱為
TG we-Calculate Editorial Team. (2026). Date Calculator — Add or Subtract Days from a Date [Online calculator]. TG we-Calculate. https://we-calculate.com/zh-tw/calculator/date-calculator
TG we-Calculate Editorial Team. "Date Calculator — Add or Subtract Days from a Date." TG we-Calculate. 2026. https://we-calculate.com/zh-tw/calculator/date-calculator.
TG we-Calculate Editorial Team, "Date Calculator — Add or Subtract Days from a Date," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/zh-tw/calculator/date-calculator
@misc{wecalculate_date_calculator, title = {Date Calculator — Add or Subtract Days from a Date}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/zh-tw/calculator/date-calculator}}, year = {2026}, note = {TG we-Calculate} }
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