Leap years exist because while the world follows a 365-day
Gregorian calendar, it actually takes the planet a little bit
more than a year to orbit the sun. It takes Earth 365 days,
5 hours, 48 minutes and 46 seconds to orbit the sun,
according to NASA — and while that is rounded down to
the 365 days we recognize as a typical year, those nearly
six extra hours don’t disappear.

Instead, leap years are added to account for the difference
and extra day keeps calendars and seasons from gradually
falling out of sync and impacting harvesting, planting and
other cycles based on the seasons. Without Leap Days, in
100 years, calendars would be 24 days off.