Add or Subtract Days Calculator
Add or subtract any number of days from a start date to find the new date and weekday.
Start date
days
Wed, Aug 12, 2026 (Wednesday)
Formula
How this is calculated
The calculator takes two inputs: a start date and N, the number of days to add. The start date is read as a local calendar date at midnight (year, month, day), and N is truncated toward zero to a whole number, since calendar dates are counted in whole-day units. A positive N moves forward in time; a negative N moves backward.
To compute the result it constructs a new date as Date(year, month, day + N), letting the calendar arithmetic roll the day count across month and year boundaries automatically. This means variable month lengths (28 to 31 days) and leap-year February 29ths are handled correctly without any manual adjustment, so adding 1 day to January 31 lands on February 1, and February counts 29 days in a leap year.
The output reports the resulting calendar date in both readable and ISO (YYYY-MM-DD) form, plus the weekday it falls on. The arithmetic is purely on calendar days: it does not count or skip weekends or holidays (use the Business Days Calculator for that), ignores time-of-day and daylight-saving shifts, and the start date itself is day zero rather than the first counted day.
Examples
| Input | Result |
|---|---|
| Start 2026-01-31, add 1 day | 2026-02-01 (Sunday) |
| Start 2026-03-01, subtract 1 day | 2026-02-28 (Saturday) |
About this calculator
The add or subtract days calculator shifts a start date forward or backward by a whole number of days. Enter a positive value to move into the future or a negative value to move into the past. The result shows the new calendar date in both a readable and ISO format, along with the weekday it lands on.
This is useful for due dates, deadlines, rental and return dates, prescription refills, warranty windows and any rule expressed as "N days after" or "N days before" a known date. Because it works on real calendar days, month lengths and leap years are handled automatically.
Frequently asked questions
Enter a negative number, such as -14, in the "Days to add" field. The result moves backward from the start date.
No. Adding 1 day to a Monday gives Tuesday; the start date itself is day zero.
The day count is rounded toward zero to whole days, since calendar dates are whole-day units. For partial days use the Time Duration Calculator.
Also known as
TG we-Calculate Editorial Team. (2026). Add or Subtract Days Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/add-days-calculator
TG we-Calculate Editorial Team. "Add or Subtract Days Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/add-days-calculator.
TG we-Calculate Editorial Team, "Add or Subtract Days Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/add-days-calculator
@misc{wecalculate_add_days_calculator, title = {Add or Subtract Days Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/add-days-calculator}}, year = {2026}, note = {TG we-Calculate} }
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