LEAP YEAR
How many people are there in the U.S. who were born on February 29?
Leaplings, those born on Leap Day, February 29, eagerly anticipate every Leap Year and the quadrennial return of their actual birth date.
According to the Social Security Administration, approximately 362,900 Americans will be celebrating their birthday today, February 29. (That’s about the population of Honolulu.) Happy leap day birthday to all of them!
This curious date in our calendar, tacked on at the end of February, only comes round once every four years, with those years being called leap years. Why do we need leap years? Because the earth takes 365 and one quarter days to go round the sun, so every four years we need an extra day for those four quarters that have built up.
That means the number of people who have a February 29 birthday is very roughly around a quarter of the population who have a “standard” birthday, which comes round every year.
More Americans celebrating their birthday on February 29 than you might expect
That number of 362,900 is curiously actually more than you might expect from the simple odds of being born on a leap day, which is 1 in 1461. Given the current US population of around 340 million you’d expect just under 233,000 leaplings, as people who celebrate their birthday on February 29 are known.
There doesn’t seem to be an official, or even obvious, explanation for why there are more people born on February 29 alive than you might expect. What’s more, the number could be expected to be even lower, as parents are generally keen to avoid their children being born on a leap day, worrying about their kids waiting four years between birthdays, being teased by classmates and hassles with documentation. That translates into 7% fewer elective cesarean deliveries on 29 February, as reported by FiveThirtyEight.
But let’s trust the official figures and go with the number of 362,900, which is indeed a pretty small fraction of the U.S. population, around 0.1%.
The next question is how many more leaplings we’ll be welcoming this year…
How many babies are born on February 29
Our estimate is that there will be 8,852 babies born in American today, February 29. That is admittedly a rough estimate, but it’s based on some pretty good assumptions.
The starting point is the annual number of births. It’s been around 3.6 million for past four years so let’s go with that.
A really simple calculation would then put the number of babies being born on February 29 at 1/366 x 3.6 million, being 9,836. BUT interestingly February is actually one of the months with a somewhat lower number of births compared to other months. February sees around 8% less births than the most popular birth months of August and September. (Yes, when it’s cold and dark outside in November and December, couples are more likely to snuggle up, and nine months later you get a little baby boom).
We’ll also need to take into account that fact that some parents are keen to avoid a February 29 birthday, so there are fewer elective caesareans.
In total we’ll adjust down by 10%, which gets us to our estimated number of babies to be born in the U.S. on February 29, 2024 of 8,852. Once we get the official stats, we’ll see how close we got.