A common year has 365 days. However, a leap year, which occurs every 4 years (with some exceptions), has 366 days. Leap years include an extra day, February 29, to keep the calendar year synchronized with the astronomical year.

Summary:

• Common year: 365 days
• Leap year: 366 days

If you want to know whether a specific year is a leap year, I can help with that too!