Count Days and Add Calendar Dates

Date counts and clock durations answer different questions. Choose the date rule that matches your task before using the answer.

Work through the task

1. For elapsed calendar days, leave Count both dates off. Start and end on the same date gives zero.
2. For a list of included dates, turn Count both dates on. This adds one to the nonnegative day difference, not to the end date.
3. To find a date a set number of days away, choose Add or subtract days. Choose a start date and enter the number of days or weeks before or after it. Weeks are seven days.
4. Read the returned date and weekday. Check any external deadline rules yourself; this calculator does not apply legal, employer or holiday conventions.

Checked examples

Calculation method

Strict Gregorian date arithmetic counts calendar boundaries without converting device-midnight timestamps into fixed 24-hour periods. Inclusive counting adds one to the day difference. Adding or subtracting a week shifts by seven calendar days.

Assumptions and limits

Supported years are 0001–9999, and a shift outside that range is rejected. Weekends and holidays are included. For clock times and months/remainders, use the separate Time Duration Calculator. Month/year shifts, working-day calendars and legal deadline rules are outside this tool.