The Islamic calendar is substantially different from the Gregorian calendar. First of all, the former is a lunar calendar while the latter is a solar one. Secondly, a year in the Islamic calendar has 11 days less than a year in the Gregorian calendar. Also, as per the Islamic calendar, a new day begins at sunset of each day, on the other hand, according to the Gregorian calendar, a new day begins at 12:00 am each night.