Why do we have leap year days? Here's a mathematical breakdown

Leap year isn’t every four years as many of us believe, according to CTV Your Morning's meteorologist Kelsey McEwen.

One year is equal to one revolution around the sun, amounting to 365.2422 days to be exact, McEwen said.

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The idea of adding a day every four years is meant to keep the calendar on track. No leap year day means approximately 5.8 hours missed every year.

McEwen said without leap day, the next century would set our calendars off by 24 days. This would result in the spring equinox – when the sun crosses the equator from south to north – no longer being in March, but in February, and 100 years later, it would be in January.

Adding in an extra day every four years doesn’t quite solve it. "That means 365.25 days, but that’s not what we’re talking about here," McEwen said.

This would mean an additional 11.2 minutes each year, and in 100 years, our calendar would be 18 hours off, McEwen explained.

The solution may be "leap year hopscotch" where we would skip a leap year if it fell on the start of a century, unless that year is divisible by 400, meaning the years 2000 and 2400 would not be skipped.

This would amount to 365.2425 days and would take 3,333 years to be one day off.

While this helps the math get closer, it’s not quite perfect, McEwen said.