A new year is upon us and it comes complete with an extra day.

Unlike most years, which have 365 days, 2024 is a leap year, which means it has 366 days. Here's what you should know about the change to your calendar:

When is the next leap year?

Leap years happen approximately every four years. This year's leap day will be on Thursday, Feb. 29, 2024.

After that, expect leap years in 2028, 2032 and 2036. Leap days will fall on Tuesday, Feb. 29, 2028; Sunday, Feb. 29, 2032 and Friday, Feb. 29, 2036.

Why do we need leap years?

While we follow the 365-day Gregorian calendar, it actually takes the Earth a bit more than a year to orbit around the sun. Without the extra day in leap years, calendars and seasons would gradually fall out of sync. That, in turn, impacts planting and harvesting.

A year based on Earth's orbit around the sun is equal to 365 days, 5 hours, 48 minutes and 46 seconds, or 365.2422 days, according to NASA. Most years, the calendar is rounded down to 365 days, but those nearly six extra hours don't disappear.

To account for the difference those hours make, an extra day is tacked onto February every leap year, giving the month 29 days instead of 28 approximately every four years.

While it's a small difference, those hours would add up over time if not for the existence of leap years.

"For example, say that July is a warm, summer month where you live. If we never had leap years, all those missing hours would add up into days, weeks and even months," according to NASA. "Eventually, in a few hundred years, July would actually take place in the cold winter months!"

The math of leap years

While leap years normally come every four years, that's not always the case. In 1582, Pope Gregory XIII reformed the calendar by specifying that all years divisible by 4 are to be leap years, with the exception of century years, which must be divisible by 400 to be considered leap years.

There's a bit of math in figuring out when leap years fall under the Gregorian calendar: The year must be divisible by four. If the year can also be evenly divided by 100, then it's not a leap year unless the year is also divisible by 400.

It's why the year 2000 was a leap year, but 2100, 2200 and 2300 will not be leap years.

Leap Year Babies

There are about 5 million people around the world who have leap year birthdays. On non-leap years, they usually celebrate on either Feb. 28 or March 1. Leap years like 2024 are particularly special since they can celebrate on the actual day.

Brianne Lutz told CBS Sunday Morning in 2012 that Leap Year Babies have a "special connection."

Notable "Leap Year Babies" born on February 29

• Composer Gioachino Rossini (Feb. 29, 1792)
• Film director William Wellman (Feb. 29, 1896)
• Band leader Jimmy Dorsey (Feb. 29, 1904)
• Singer Dinah Shore (Feb. 29, 1916)
• Ballet dancer James Mitchell (Feb. 29, 1920)
• "Godfather" actor Alex Rocco (Feb. 29, 1936)
• Serial killer Aileen Wuornos (Feb. 29, 1956)
• Motivational speaker Tony Robbins (Feb. 29, 1960)
• Rapper Ja Rule (Feb. 29, 1976)
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