how many days in a year exactly

A year is not exactly 365 days. A common year has 365 days, while a leap year, which occurs almost every four years, has 366 days. The reason for this variation is that the Earth's orbit around the Sun actually takes about 365.242199 days on average (365 days, 5 hours, 48 minutes, and 46 seconds). To keep the calendar year synchronized with the astronomical year, the Gregorian calendar includes leap years where an extra day is added to February. Over a 400-year cycle, the average length of a year in the Gregorian calendar is 365.2425 days.