As you schedule events in life a date calculator can be a handy utility. This calculator can display a calendar for any month and year, provide information about a specific day, find a day, or calculate information about the interval between two dates. To use the calculator simply select a calculation from the list and enter a date (and other information as needed). A calendar is a system to organize the days of the year. All calculations in this app are based on the Gregorian calendar. For civil and commercial purposes, the calendar most commonly used throughout the world today is the Gregorian calendar. The Gregorian calendar was first introduced by Pope Gregory XIII in 1582. It was a modification of the Julian calendar and better accounts for the length of the solar year (365 days, 5 hours, 48 minutes, and 46 seconds).