Calculate days between two dates, add or subtract days (including business days) from any date. Free online date and calendar tools.
When checked, the end date is counted (e.g. Feb 10–May 23 = 103 days). When unchecked, the end date is excluded (102 days). Total will always match weekdays + weekend days.
Select both dates to see the number of days between them.
Enter start date and at least one amount (years, months, weeks, or days) to see the result.
When checked, the end date is included in the count. When unchecked, only days between start and end are counted.
Select start and end dates to see the duration.
This date calculator helps you find the number of days between two dates and to add or subtract a number of days, weeks, months, or years from any date. You can optionally use business days (weekdays only) when adding or subtracting days. Below you will find detailed information about the Gregorian calendar, leap years, and how dates are used in daily life and business.
The Gregorian calendar is the calendar used in most of the world today. It was introduced by Pope Gregory XIII in 1582 to correct the drift of the older Julian calendar relative to the solar year. The Julian calendar had a leap year every four years without exception, which made the average year slightly too long. Over centuries, this caused the calendar to drift relative to the seasons.
The Gregorian calendar keeps a leap year every four years, but omits leap years in century years unless the year is divisible by 400. So 2000 was a leap year, but 1900 and 2100 are not. This rule brings the average length of the year very close to the actual tropical year (about 365.2422 days), so the calendar stays aligned with the seasons over long periods.
The calendar has 12 months: January (31 days), February (28 or 29 in leap years), March (31), April (30), May (31), June (30), July (31), August (31), September (30), October (31), November (30), and December (31). The total is 365 days in a common year and 366 in a leap year.
A leap year has 366 days instead of 365. The extra day is added as February 29. Leap years exist because the Earth takes about 365.25 days to orbit the Sun. Without an extra day every four years, the calendar would drift by about one day every four years, and over time the seasons would fall in the "wrong" months.
In the Gregorian calendar, a year is a leap year if it is divisible by 4, except that century years (e.g. 1900, 2100) are not leap years unless they are divisible by 400. So 2024 and 2028 are leap years; 1900 is not; 2000 is. When you calculate "days between two dates" or "add 30 days," the calculator automatically accounts for leap years and varying month lengths.
Calendars have been used for thousands of years to organize time for agriculture, religion, and administration. The ancient Egyptians used a solar calendar; the Romans developed the Julian calendar under Julius Caesar. The Gregorian reform in 1582 was adopted first by Catholic countries and gradually by others; Great Britain and its colonies adopted it in 1752, and some countries only in the 20th century.
Today, the Gregorian calendar is the international standard for civil use. Other calendars (e.g. Islamic, Hebrew, Chinese) are still used for religious or cultural purposes and often run in parallel with the Gregorian calendar for dating events.
Business days are typically Monday through Friday—the days when most offices and institutions are open. In this calculator, "business days" means weekdays only: we count only Monday–Friday and skip Saturdays and Sundays. This is useful for deadlines (e.g. "10 business days from today"), contract periods, or delivery estimates.
Public holidays are not automatically excluded; the definition of a holiday depends on the country and region. For legal or official deadlines, always check the rules that apply to your situation. This tool is intended for general planning and education.
A "date" (e.g. January 15, 2025) can refer to different moments in time in different parts of the world. When it is midnight in London, it is still the previous day in Los Angeles. This calculator works with calendar dates only (year, month, day) and does not use time or time zone. For "days between" or "add days," we count full calendar days. If you need to account for a specific time zone, consider which date applies in that zone at the relevant time.