How to use the date difference calculator
- Choose days between two dates or add or subtract days.
- Pick the dates. The start date is today by default.
- To count both the first and last day, switch on include the end date.
- To go back in time, enter a negative number in add/subtract mode.
How it is calculated
Days = End date − Start date (+1 if the end date is included) Weeks = Days ÷ 7 (remainder = extra days) Months = whole months from the start date, then leftover days Weekdays = days that fall Monday–Friday
Worked examples
- Days until Christmas: January 1 to December 25, 2026 = 358 days (51 weeks and 1 day).
- Counting both days: a festival from October 1 to October 31 runs 31 days, of which 22 are weekdays.
- 90-day deadline: 90 days after October 24, 2026 is Friday, January 22, 2027.
- Leap year: February 1 to March 1, 2024 = 29 days (exactly 1 month).
Common day counts
| Period | Days |
|---|---|
| 1 week | 7 |
| 1 month | 28–31 |
| 3 months (a quarter) | 89–92 |
| 6 months | 181–184 |
| 1 year | 365 (366 in a leap year) |
| Average year (Gregorian) | 365.2425 |
| Pregnancy (from last period) | about 280 (40 weeks) |
Where a date calculator helps
- Countdowns: days until a holiday, wedding, vacation, exam or retirement.
- Deadlines: return windows (30 days), notice periods, warranty periods and contract terms.
- Legal and finance: interest periods, statute-of-limitation dates and grace periods — check whether business days or calendar days apply.
- Health: medication courses, recovery periods, quarantine periods and pregnancy due dates.
- Personal: anniversaries, how long you have lived somewhere, or streaks and habits.
- Projects: sprint lengths and milestones. For working days, use the business days calculator.
Inclusive vs exclusive counting
Date counts often differ by one day depending on whether both ends are counted. “From Monday to Friday” is 4 days apart, but an event that runs Monday through Friday lasts 5 days. Hotel nights are counted without the check-out day; rentals and leave requests often count both. When an agreement or law sets a deadline, read its wording: “within 30 days” usually means the day after the starting event is day 1.
Months are not all equal
Because months have different lengths, “one month later” is not a fixed number of days. This calculator moves to the same date in the next month, and when that date doesn’t exist (like February 30) it uses the last day of the month. The total days figure is always exact, so use it whenever precision matters.
Dates are entered in the international YYYY-MM-DD order behind the scenes, so there is no confusion between the US month/day format and the day/month format used in most other countries.