Add or subtract from a date
Choose a start date and a whole number to add or subtract.
Days between two dates
Choose a start and end date to count the days between them.
How the date calculator works
Days and weeks are added one calendar day at a time, so the result is the same whatever your time zone and however the clocks change for daylight saving. Months and years keep the day of the month where they can; when the target month is shorter, the result is that month's last day.
Business days skip Saturdays, Sundays and US federal holidays on the day they are observed. That is the usual way to count deadlines such as "10 business days" for a delivery or a reply. Check the full holiday lists if your office closes on other days too.
Worked examples
- Jan 1, 2027 + 90 days = Thursday, April 1, 2027A 90-day deadline from New Year
- Jan 31, 2027 + 1 months = Sunday, February 28, 2027One month after 31 January lands on the last day of February
- Dec 24, 2026 + 10 business days = Monday, January 11, 2027Ten business days, skipping Christmas and New Year
- Mar 15, 2027 − 6 weeks = Monday, February 1, 2027Six weeks before a date
- Feb 29, 2028 + 1 years = Wednesday, February 28, 2029One year after a leap day
Date Calculator FAQ
How do I add days to a date?
Enter the start date, choose Add, type the number of days and leave the unit on days. The calculator moves forward one calendar day at a time, so 90 days after January 1, 2027 is April 1, 2027. To go back in time, choose Subtract.
What happens when I add a month to January 31?
Months have different lengths, so the result moves to the last day of the shorter month: January 31 plus one month is February 28 (or February 29 in a leap year). Adding a year to February 29 gives February 28.
What counts as a business day?
Monday to Friday, excluding US federal holidays on their observed dates. If you start on a weekend or holiday, adding one business day gives the next working day.
How many weeks are in a year?
A year has 52 weeks plus one day, or plus two days in a leap year. In the ISO week system some years, such as 2026, have 53 numbered weeks.
Can I calculate the time between two dates?
Yes. Use the second calculator on this page, or the days between dates tool, to count the days, weeks, weekdays and working days between any two dates.