Why Thursday is a leap day

"Without the leap years, after a few hundred years we will have summer in November"

(Image credit: Gam1983 / iStock / Getty Images Plus)

published 26 February 2024

What happened?

Don't call it a bonus day. But every leap year, we get a 29th day in February.

Julius Caesar, "dealing with major seasonal drift" in Roman calendars, introduced the Julian calendar in 46 BCE, counting a year as 365.25 days and adding an extra day every four years, The Associated Press said. But a year is actually 365.242 days, so Pope Gregory XIII knocked out a leap year every hundred years — except years divisible by 400, like 2000. The 1582 Gregorian calendar "remains in use today" and, while its "gnarly math" is not perfect, it reduced "drift to mere seconds."

"Without the leap years, after a few hundred years we will have summer in November" and Christmas in summer, said Younas Khan, a physics instructor at the University of Alabama at Birmingham. Some people treat Feb. 29 "as a free day" to do things "they've long been putting off," Phil Plait said at Scientific American. "I think that's a pretty good idea because, after all, catching up is what leap day is all about," astronomically speaking.

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Peter has worked as a news and culture writer and editor at The Week since the site's launch in 2008. He covers politics, world affairs, religion and cultural currents. His journalism career began as a copy editor at a financial newswire and has included editorial positions at The New York Times Magazine, Facts on File, and Oregon State University.