How to find the resulting date
Enter a start date, choose Add days or Subtract days, and enter a nonnegative whole number of days. Select Calculate to see the resulting date in YYYY-MM-DD format. Try example fills the fields without calculating. Reset clears the date and day count, and restores Add days.
The start is day zero. Adding 1 means the next date; subtracting 1 means the previous date. Adding or subtracting 0 leaves the date unchanged. Changing the operation clears the day count so you can enter a new calculation.
Method and examples
The calculator checks the start date, counts it as a whole UTC day number, then adds or subtracts the days you entered to find the new date. This follows the ECMAScript Gregorian calendar model. setUTCFullYear preserves years 0001–0099 without a 1900 offset. Results are exact dates; no rounding is applied.
| Start date | Operation | Result |
|---|---|---|
| 2024-02-28 | Add 2 days | 2024-03-01 |
| 2024-03-01 | Subtract 2 days | 2024-02-28 |
| 2024-02-29 | Add 0 days | 2024-02-29 |
| 2024-12-31 | Add 1 day | 2025-01-01 |
| 0099-12-31 | Add 1 day | 0100-01-01 |
Assumptions and limits
Every calendar date counts, including weekends, public holidays and leap days. The tool uses the Gregorian calendar throughout years 0001–9999, including historical dates before local adoption. Start and result must stay in that range; impossible dates such as February 29, 2023 are rejected.
The day count must be a whole number from 0 to 3,652,058, the greatest distance within the supported range. A smaller count can still exceed the range near either boundary. Use the operation control to subtract instead of entering a negative number.
This calculation has no clock times or local time zones. It does not calculate working days or apply court, employment, tax or contract deadline rules. For those tasks, confirm the required calendar and counting convention separately.
Related tools
If you know both dates, use Date Difference to count elapsed days or include both dates. For clock-time intervals, use Time Duration.