Date Calculator
A date calculator counts the days between two dates or finds the date a set number of days away. From 1 March to 9 June is 100 days, or 14 weeks and 2 days. It also counts weekdays (Monday to Friday), which is how most business deadlines are measured.
Counts calendar days from the start date up to, but not including, the end date. Weekdays exclude Saturdays and Sundays.
How to use the Date Calculator
- Choose Days between or Add days.
- For Days between, pick a start date and an end date.
- For Add days, pick a start date and enter the number of days; use a negative number to go back.
- Read the days, weeks and weekdays, or the resulting date with its weekday.
Formula
days = end date - start date · weekdays = days that fall Monday to FridayDates are compared at midday local time, so daylight saving changes never shift the count. Weekdays are counted from the start date up to, but not including, the end date. Public holidays are not excluded.
Common uses
- Project deadlines and delivery dates.
- Notice periods, warranties and returns windows.
- Countdowns to holidays, exams and events.
- Pregnancy, training plans and other day-based schedules.
- Age in days, or time since a past event.
Days versus months
Adding days is exact, while adding months follows the calendar: one month after 31 January can only be 28 or 29 February. For contracts written in months, count on the calendar; for anything written in days, use this calculator.
Date Calculator questions
How do I calculate the number of days between two dates?
Choose Days between, then enter a start date and an end date. The calculator shows the total days, the same span in weeks and days, and how many weekdays it contains. If the end date is before the start date, the result is negative.
How do I count business days between two dates?
Read the Weekdays result, which counts Monday to Friday and skips Saturdays and Sundays. For example, Monday 5 January to Monday 12 January contains 5 weekdays. Public holidays are not removed automatically, so subtract any that fall inside your range.
How do I add or subtract days from a date?
Choose Add days, pick the starting date and type the number of days. Enter 90 to find the date 90 days later, or -30 to go back 30 days. The result includes the weekday, which helps when a deadline lands on a weekend.
What is the difference between adding days and adding months?
Adding days moves an exact number of 24-hour days; adding months follows the calendar and varies in length. Thirty days after 31 January is 2 March in a non-leap year, while "one month later" is usually read as 28 or 29 February. Check which one your contract or policy uses.
How do I calculate my age in days?
Choose Days between, enter your date of birth as the start date and today as the end date. The result is your age in days, and the weeks figure shows the same span in weeks. Leap years are included automatically because real calendar dates are used.
Does the calculator include the end date?
No. It counts the number of days from the start date to the end date, so 1 March to 2 March is 1 day. If you need an inclusive count, for example for a booking that covers both dates, add 1 to the result.
How do I plan a project backwards from a deadline?
Start from the deadline and use Add days with a negative number for each phase. For a launch on 1 December with 20 days of testing, enter -20 to find when testing must start. Leave buffer time for reviews and holidays.
Which date format should I use?
The date picker uses your browser's local format, so you never type a format by hand. When sharing dates internationally, write them as YYYY-MM-DD (ISO 8601), for example 2026-03-01, which avoids confusion between day-first and month-first formats.