Add Days Calculator

How to add days to a date

1. Choose the start date. The field opens on today's date.
2. Type the number of days to add. Use a negative number, such as -30, to move backwards in time.
3. Press the button. The calculator shows the new date and the weekday it falls on.

Doing it by hand means carrying across months of unequal length. For example, 30 days after 18 March 2026 is not 18 April. March has 31 days, so 13 days remain in March after the 18th, and the other 17 fall in April: the answer is 17 April 2026, a Friday. The calculator does that bookkeeping for you, including February 29 in leap years.

Only whole days are accepted. A fraction of a day, such as 1.5, is rejected. To work with hours and minutes, use the time calculator.

Practical uses

• Payment terms. An invoice dated 18 March 2026 with net 30 terms falls due on 17 April 2026.
• Deadlines and notice periods. A 90-day notice period that starts on 20 November 2026 ends on 18 February 2027.
• Looking back. To find the date 120 days before 15 January 2027, enter -120. The answer is 17 September 2026.
• Returns, warranties and trials. Add the length of the window to the purchase date to see the last day it applies.
• Project planning. Convert a duration in calendar days into a delivery date.

These counts include weekends and holidays. If you need business days only, use the working days calculator. To measure the gap between two known dates instead, use the days between dates calculator.

What day will it be in X days?

The weekday repeats every seven days, so only the remainder when you divide the days by 7 matters. Adding 14 or 70 days never changes the weekday. Adding 365 days moves it forward one day (365 = 52 × 7 + 1) and in a span that includes February 29 it moves forward two.

The table counts from Friday, 1 January 2027.

Leap years show up quickly in longer spans. Ten days after 20 February 2027 is 2 March 2027, but ten days after 20 February 2028 is 1 March 2028, because 2028 has a 29 February.

Which calendar is used

The calculator uses the Gregorian calendar for every date, extended backwards and forwards without limit (the proleptic Gregorian calendar). A year is a leap year when it is divisible by 4, except for century years, which must be divisible by 400. So 2000 and 2400 are leap years, while 1900 and 2100 are not.

Historical dates before a country adopted the Gregorian calendar, which happened at different times between 1582 and the 20th century, will differ from the dates people recorded then. Years before year 1 are shown with a minus sign, and year 0 is included, matching the ISO 8601 convention for dates.