Add Days to a Date
Find the date you get by adding or subtracting a number of days from a start date.
A negative number moves backward in time.
Enter a start date to run the calculation.
How is this result calculated?
The resulting date is calculated by adding the entered number of days to the start date: result_date = start_date + number_of_days. The calculation is done in UTC time based on the year/month/day components of the start date, to avoid any offset caused by the local time zone or daylight saving changes.
A negative number of days moves the date backward instead of forward. A number of days field left empty is treated as 0: the resulting date is then identical to the start date.
Frequently asked questions
How does a negative number of days work?+
A negative number moves the start date backward instead of forward: for example, -10 days from January 15 gives January 5. It's the same calculation as for a positive number, simply applied in the other direction.
What's the difference with the days between two dates calculator?+
This calculator starts from a single date and a number of days to find a new date. The days between two dates calculator does the opposite: it starts from two already known dates to calculate the gap in days between them. See also /jours-entre-deux-dates.
Does this calculator count calendar days or business days?+
Calendar days: every day counts, including weekends and public holidays. To add only business days, excluding weekends (and French public holidays if needed), use the dedicated calculator at /ajouter-jours-ouvres.
How is a change of month or year handled?+
The calculation is based on the full arithmetic of dates (year, month, day), not on a simple day counter within the current month. An addition that crosses a month boundary, including a year-end or a leap year, is therefore handled automatically and correctly.
What is this calculator useful for?+
Calculating a deadline, a contractual delay, a reminder date, or any situation where you know a start date and a number of days to add or subtract.