What Is a Leap Year? An Etymological Perspective

February usually has 28 days. But here we are on the February 29 because 2020 is a leap year! But what exactly is a leap year? Why does it give us an extra day? And where does this term come from? Let’s take a look.

What Is A Leap Year?

We have leap years because our regular calendar year (365 days) doesn’t quite match a solar year (i.e., the time it takes for the Earth to orbit the Sun, or 365.2422 days). This means the calendar year is faster than a solar year.

If left uncorrected, the seasons would thus gradually creep forward each year. Admittedly, this would be a slow process (we would drift forward about 25 days every 100 years). But it would still be confusing!

To stop this, we add an extra day to the end of February every four years. As such, any year that can be divided by four is a leap year, which means there are 29 days in February instead of the regular 28.*

Where Does the Term Come From?

The “leap” in “leap year” literally means “jump.” But what are we jumping?

To understand this, we first need to know that fixed dates usually move forward one day every year. For example, Christmas Day was on a Tuesday in 2018 and a Wednesday in 2019. If 2020 had the regular 365 days, we’d expect Christmas to be on a Thursday this year. But since 2020 has 29 days in February, we “leap” forward an extra day and Christmas will be on a Friday.

The “leap” in leap year, then, reflects the calendar jumping forward one day.

If you have any questions, just leave a comment below this post. And if you have any documents that you need proofreading, we have editors available 24 hours a day, 365 days a year (or 366 on a leap year).

* Since we don’t lose exactly a day every four years, centennial years not divisible by 400 (e.g., 1700, 1800, 1900) are actually common years with 365 days. This keeps everything roughly in sync, but it’s a complicated system and probably not something to worry about unless you’re designing a very long-term calendar.