Date Calculator

Result date
ISO date
Weekday
Calendar days
Direction

Calculate calendar dates without converting them to approximate month or year lengths. Add or subtract a duration, find the exact difference between dates, or count working days.

Choose a calculation mode first. For a date a certain number of days ahead, set years, months, and weeks to zero and enter the number of days.

Calendar-aware date arithmetic

Years and months are applied before weeks and days. When the destination month is shorter, the day is clamped to the final valid day of that month. For example, adding one month to January 31 produces the last day of February.

Date difference and business days

Date difference reports both a calendar duration and exact elapsed days. Business day mode treats Monday through Friday as working days, supports inclusive or exclusive boundaries, and removes valid custom holiday dates that fall on weekdays.

How to calculate dates

  1. To add or subtract days, choose Add or subtract, enter the start date, set years, months, and weeks to zero, and enter the days.
  2. To count elapsed days, choose Date difference and enter the start and end dates. Read Total days below the calendar duration.
  3. For working days, choose Business days. Check the endpoint options and enter any holidays as YYYY-MM-DD, separated by commas or line breaks.

Date Calculator FAQ

How do I find the date 30 days from a starting date?

Choose Add or subtract and Add. Enter the starting date, set years, months, and weeks to zero, and enter 30 days. The result includes the date and weekday; the starting date is day zero.

Are the start and end dates included?

Date difference gives elapsed days: January 1 to January 2 is 1 day. To count both dates, add 1 to the absolute day difference yourself. Business days has separate checkboxes to include the start and end dates.

What happens when a month does not have the same day?

The result uses the last valid day of the target month. January 31 plus one month is February 28, or February 29 in a leap year. Years and months are applied before weeks and days.

Are public holidays excluded automatically?

No. Business days excludes Saturdays and Sundays. Enter the holidays you want excluded as YYYY-MM-DD, separated by commas or line breaks. A holiday on a weekend is not deducted twice.

Related date calculations: Date Calculator · Days Between Dates · Add Days to Date · Business Days