Quick question: What are the chances a given person will be born on February 29, a.k.a. a leap day or leap year day? Depending on who you ask (and what century it is), the odds are either one in 1461 or one in 1506. In short, the answer is complicated—just like a lot of other things about this curious calendar date.

1. Julius Caesar understood the need for leap years.

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Established in the year 46 BCE, the so-named Julian calendar was devised by Julius Caesar and the Greek astronomer Sosigenes of Alexandria. By this point in history, the traditional Roman calendar had fallen out of sync with the seasons. So at Caesar’s request, Sosigenes reformed it. One of his major changes was the implementation of leap years: Every fourth year, February would receive an extra day. This was meant to keep the new calendar in alignment with the Earth’s position relative to the Sun. Unfortunately, the whole system fell prey to a miscalculation and ended up including too many leap years.

2. The Julian Calendar didn’t exactly fix the leap year problem.

Like many of his contemporaries, Sosigenes believed that each solar year (the amount of time between successive vernal equinoxes) lasted for 365.25 days. Yet this isn’t quite right; as we now know, they last for approximately 365 days, five hours, 48 minutes, and 45 seconds (ie: 365.24219 days) apiece. Over time, the discrepancy spelled trouble. By 1577, the Julian calendar had fallen 10 days out of alignment, meaning important Christian holidays weren't being celebrated on the proper dates. This prompted Pope Gregory XIII to take action. A commission was established to modify the old calendar and upgrade the leap year system. Thus, the new and improved Gregorian calendar was born. It was first implemented in 1582, and we’re still using it today.

3. Sometimes, we skip leap years.

Under Gregorian calendar rules, certain leap years get skipped. "Century years” like 1700, 1800, and 1900 did not receive leap days, lasting for just the standard 365 days. However, if a given century year is divisible by four, it still gets a leap day, and is thus a bona fide leap year. That’s why 2000 CE was considered a leap year, but the year 2100 CE won’t be.

4. There’s a centuries-old tradition of women proposing to men on leap days.

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How this whole trend got started is pretty murky. Saint Patrick was rumored to be an early proponent, and there’s a contentious claim that in 1288 Queen Margaret of Scotland—who was only five at the time—legalized a fine for men who turned down a woman’s leap day marriage proposal. Regardless, the custom has a long history in places such as Ireland, where leap day is also called Bachelor’s Day.

5. There's an Honor Society of Leap Year Day Babies for people born on February 29.

“Membership in the society is free, but is restricted to people born on Leap Year Day,” explains the group’s official website. Launched in 1997, the HSLYDB now boasts more than 11,000 members from all over the world. For many of them, a shared pet peeve is websites that consider February 29 an invalid birth date. The HSLYDB has successfully taken Microsoft and YouTube to task over this very issue. It’s also been fighting to get "leap year day" capitalized in dictionaries and acknowledged on calendars. (That fight is still a work in progress.)

6. February 29 has a connection to the Salem Witch Trials.

February 29, 1692, was a dark day in colonial Massachusetts. That’s when the first arrest warrants were issued for what became known as the Salem Witch Trials. By the end of these paranoia-induced hearings and prosecutions, 20 people were executed.

7. Toys “R” Us once came under fire for ignoring leap year kids.

Toys "R" Us invited kids to sign up for personalized birthday cards from store mascot Geoffrey the Giraffe. Sounds cute, right? Well there was a time when leap day babies were left out of the fun due to a programming issue. “How do you explain to a five-year-old that they won’t receive a birthday card from Geoffrey over at Toys "R" Us this year, because the Toys "R" Us computer has no way to recognize their birthday?” asked HSLYDB co-founder Raenell Dawn in 2008. The problem was promptly fixed.

8. Rapper Ja Rule is a leap day Baby.

Rapper Ja Rule attends at Caesars Palace in Las Vegas, Nevada.
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Variously called leapers, leaplings, twenty-niners, and leap day babies (LDBs), people who came into the world on February 29 are in good company. In addition to Ja Rule, these folks share their birthday with baseball great Pepper Martin and former Indian Prime Minister Morarji Desai.

9. A community on the Texas-New Mexico border calls itself the “Leap Year Capital Of The World.”

Anthony, Texas and Anthony, New Mexico bookend the dividing line between their respective states. In 1988, local leapers Mary Ann Brown and Birdie Lewis proposed the greater Anthony area should throw a Worldwide Leap Year Festival on their shared birthday—and did so for several more leap years. The parties featured parades, tours, southwestern dancing, and of course, birthday cake. Past shindigs have attracted LDBs from across the globe—along with thousands of other guests. According to the event's website, they're still looking for a 2020 sponsor, so no details have been confirmed.

10. Movie history was made on February 29, 1940.

At the 1940 Academy Awards, Hattie McDaniel’s performance as Mammy in Gone with the Wind earned her an Oscar for Best Supporting Actress. She was the first African American to win this particular accolade.