How many days are there in a year common and Leap ? Ans. Common 365 days and Leap 366 days. The true length of a year on Earth is 365.2422 days, or about 365.25 days. We keep our calendar in sync with the seasons by having most years 365 days long but making just under 1/4 of all years 366-day "leap" years. #general #knowledge #earth #education