Calendar Calculator

Using the calendar calculator

Start by choosing the calculation. Add / subtract time takes a starting date and returns a new date. Time between dates takes two dates and describes the span between them. Leave the starting date empty to use today.

• Add / subtract time. Pick Add to date or Subtract from date, then fill in any of the Days, Weeks, Months and Years boxes. You can use several at once.
• Time between dates. Enter a starting date and an end date, and choose whether the last day should be counted. The dates may be given in either order.

Adding and subtracting time from a date

Years, months, weeks and days are combined into a single shift. Whole years and months move the calendar, and weeks count as seven days each. Fractions are dropped, so 1.5 months counts as 1 month.

Example. Start on 19 October 2026 and add 1 year, 1 month, 2 weeks and 10 days. One year takes you to 19 October 2027 and one month to 19 November 2027. Two weeks and ten days are 24 days, which reaches 13 December 2027.

Subtracting. Taking the same 1 year, 1 month and 10 days away from 19 October 2026 lands on 9 September 2025.

Time between two dates

The result is shown four ways so you can use whichever fits: the number of days, the span as years, months and days, the span in weeks with the leftover days, and the number of whole months.

Example. From 19 October 2026 to 5 January 2030 there are 1,174 days. As a calendar span that is 3 years, 2 months and 17 days. In weeks it is 1,174 ÷ 7 = 167.71, which is 167 weeks and 5 days, and 38 whole months fit inside it.

weeks = days ÷ 7 whole weeks = ⌊days ÷ 7⌋ leftover days = days mod 7

Including the last day. Counting from one date to another normally leaves out the final day, in the same way that 1 June to 2 June is one day. Switching Include last day to Yes adds one day, as when you count calendar days in a hotel stay or a booking that covers both the first and last date. For the example above, the span becomes 1,175 days, or 3 years, 2 months and 18 days.

To count only weekdays, see the working days calculator. For a dedicated day count, try the days between dates calculator.

Common time intervals

Handy conversions when you plan a date range by hand:

A common year is 52 weeks plus 1 day and a leap year is 52 weeks plus 2 days, which is why a date moves forward one weekday each year, or two after a leap day. The Gregorian calendar averages 365.2425 days per year, and its 400-year cycle holds exactly 146,097 days, or 20,871 whole weeks, so weekdays repeat in the same pattern every 400 years.

For hours and minutes use the time calculator, and to learn the weekday of any date open the weekday calculator. The add days calculator is a simpler option when only days are involved.