Add or subtract days

Find a date before or after your starting point

Use this calculator when you know an interval and want the date at the other end. You might need a follow-up thirty days after an appointment, a reminder two weeks before a trip, or the end of a ninety-day planning window. Start with the actual date of the event; it does not have to be today.

1. Choose a starting date

   Select the date you want to count from. Check the year when planning across December and January.

2. Choose add or subtract

   Add moves into the future. Subtract moves into the past. Enter the distance as a positive whole number in either direction.

3. Enter the number of days

   Select Calculate to see the resulting date and its weekday. Zero returns the starting date.

Examples you can check on a calendar

For the thirty-day example, 14 September is the starting point, or day zero. The next date, 15 September, is one day later. Continue counting forward and day thirty is 14 October. If your instruction instead says that 14 September is “day one”, the thirtieth included date is one day earlier. Decide which convention applies before entering the interval.

Calendar days include weekends

Every calendar day advances the count, including Saturdays, Sundays, and public holidays. Adding seven days always moves to the same weekday in the following week. Adding thirty days is different from adding one calendar month because months contain different numbers of days. This form adds days only; it does not apply a month-end rule for monthly subscriptions or recurring appointments.

Working backward from a deadline

Suppose an event is scheduled for 14 September and preparation needs fourteen calendar days. Subtract fourteen to find 31 August as the starting point. Then check whether your team can work during the intervening weekends. If the schedule is measured in working days, use the business days calculator to check an interval and account for public holidays separately.

For a project with several dependent tasks, calculate each milestone from an agreed starting point and write down the assumptions. A task that takes three days of effort may occupy more than three calendar days if people are unavailable. The project timeline guide explains how to turn those individual dates into a workable schedule.

Input limits and useful cross-checks

Enter a whole number between zero and 3,000,000. The starting and resulting dates must stay within years 1 through 9999, so a large interval near either boundary may be rejected. To check an ordinary result, put the starting and resulting dates into the date difference calculator; the distance should match the number you entered.