Shift a date forward or backward
- Choose a start date and Add or Subtract.
- Enter a nonnegative whole number of calendar days and calculate.
- Review the ISO result, weekday and signed shift, then copy or download the result.
Examples and counting convention
2024-02-28 plus 1 day is 2024-02-29; plus 2 days is 2024-03-01. Subtract 1 day from 2024-03-01 to get 2024-02-29. Subtract 1 day from 2024-01-01 to get 2023-12-31. A zero-day shift returns the start date in either operation.
The start date is day 0. Each day is a calendar step; weekends and holidays count. Subtraction shows a negative signed shift, addition a positive shift, and zero stays zero. Adding or subtracting 7 days keeps the weekday.
Leap years follow the Gregorian rule. Century years must be divisible by 400: 1900 and 2100 are not leap years, while 2000 is. Day of year is 1 on January 1 and 365 or 366 at year end.
Limits and privacy
Start dates and results must be within 0001-01-01 to 9999-12-31. Day count 0–3,652,058, whole numbers only; the maximum usable count depends on start date and operation. Out-of-range results produce an error rather than a clipped date. Gregorian rules are applied even before historical adoption.
Date-only arithmetic ignores local time, time zones and daylight-saving transitions. It does not compute elapsed hours or business days and does not establish a legal deadline. Inputs stay in browser memory without uploads or saved dates. CSV contains operation, entered days, signed shift, ISO start/result, weekday and day of year. Use result as start date copies the calculated date into Start and clears the previous result; the day count and direction stay selected. Reset restores addition and example inputs and clears results. Undo action restores the date, day count and direction before Today, Reset or Use result; calculate again to review the restored entries. Editing starts a new state.
Should I enter a negative number to subtract?
Choose Subtract and enter a nonnegative day count. The operation determines the direction.
Does adding or subtracting 1 day include the start date?
The start is day 0. One day moves to the next or previous calendar date. An inclusive range count is a different operation.
Are weekends skipped?
No. Every calendar day counts.