Date Difference & Duration Calculator

Calculating the exact number of days between two calendar dates is incredibly tedious to do manually due to the varying lengths of months and the erratic injection of leap years. Our Date Calculator perfectly handles Gregorian calendar math to give you the exact duration.

The Gregorian Calendar & Leap Years

Introduced by Pope Gregory XIII in 1582, our current calendar is designed to keep us aligned with the Earth's revolutions around the Sun (which takes approximately 365.2425 days). To account for that decimal, we add an extra day (Feb 29) every 4 years.

However, to prevent over-correcting, a year that is exactly divisible by 100 is not a leap year, unless it is also divisible by 400. (This is why the year 2000 was a leap year, but 1900 was not!). Our javascript calculator automatically factors in all of these centuries-old rules when computing your dates.

Common Uses for this Calculator

• Project Management: Finding the exact number of days remaining until a software launch or construction deadline.
• Finance & Legal: Calculating interest maturation dates or the expiration of a 90-day contract clause.
• Personal Milestones: Figuring out exactly how many days old you are, or counting down to a wedding or vacation.