Day & Date Calculator
Calculate exact durations between dates, add or subtract calendar and business days to find future/past deadlines, and look up leap years and Julian days.
📆 Date Ranges
Duration📊 Time Calculation
Span ResultsUnderstanding Date & Time Calculations
Calendar Days vs. Business Days
**Calendar Days** count every single consecutive 24-hour period on the calendar, including weekends and holidays. **Business Days** represent only standard working days (Monday through Friday), skipping Saturday and Sunday. In project management, business days are essential for calculating contract deadlines, shipping intervals, and financial clearing schedules.
The Leap Year Rule
A leap year has 366 days instead of 365, adding February 29th to align the calendar year with the astronomical solar year. Under the Gregorian calendar rules, a year is a leap year if it is exactly divisible by 4, except for century years (ending in 00), which are only leap years if they are also exactly divisible by 400. E.g., 2000 was a leap year, but 1900 and 2100 are common years.
What is the Julian Day Number?
The **Julian Day Number (JDN)** is the integer number of days elapsed since the start of the Julian Period (January 1, 4713 BC). Astronomers and historical chronologists use this continuous fractional scale to calculate time elapsed between two distant events without having to deal with changes in calendar structures (such as switching from Julian to Gregorian dates).