Earth orbits the sun once every 365.25 days. Since our calendar years have only 365 days, we add an extra leap day every four years to account for the difference. Though we can't feel it ...

It takes 365 ¼ days for the earth to rotate around the sun. But the calendar year is 365 days. So, to synchronize the calendar year with the solar year, we add an extra day every four years.

The time taken for Earth to orbit the Sun is actually closer to 365.25 days ... is approximately 29.5 days. Calendar months are based on this and vary between 28 and 31 days in length.