The typical number of days in a leap year is 366 days. Leap years occur every four years to help synchronize the calendar year with the solar year, which is about 365.2425 days long. The additional day is added to February, extending it from 28 to 29 days. However, there are exceptions: a year must be divisible by four to be a leap year, but if it's divisible by 100, it must also be divisible by 400 to qualify. This system ensures that our calendar remains aligned with Earth’s orbit around the sun.