The most common birthday in the United States is September 9. Between 1994 and 2014 an average of 12,344 babies were born on that date each year. The rarest birthday is February 29, because it only happens once every four years. Among dates that happen every year, December 25 is the least common, with an average of 6,601 births.
Where these numbers come from
The rankings use two public datasets that FiveThirtyEight published on GitHub. One comes from the CDC's National Center for Health Statistics and covers 1994 to 2003. The other comes from the Social Security Administration and covers 2000 to 2014. We used the CDC file for 1994 to 1999 and the SSA file for 2000 to 2014, then averaged each calendar date across the 21 years. That is the same method behind the widely shared FiveThirtyEight chart, and our top five matches it.
Across those years the US averaged 11,175 births a day, about 85.7 million births in total. Any date well above that average is a common birthday. Any date well below it is a rare one.
The most common birthday dates: top 10
Rank | Birthday | Average births per year |
|---|---|---|
1 | September 9 | 12,344 |
2 | September 19 | 12,285 |
3 | September 12 | 12,282 |
4 | September 17 | 12,201 |
5 | September 10 | 12,190 |
6 | September 20 | 12,162 |
7 | July 7 | 12,147 |
8 | September 15 | 12,126 |
9 | September 16 | 12,114 |
10 | September 18 | 12,112 |
Nine of the top ten fall in September. The only exception is July 7, at 7th. December 20 is just outside the list at 11th, and August 8 is 15th.
The least common birthdays: bottom 10
Rank | Birthday | Average births per year |
|---|---|---|
366 | December 25 | 6,601 |
365 | January 1 | 7,827 |
364 | December 24 | 8,103 |
363 | July 4 | 8,825 |
362 | January 2 | 9,356 |
361 | December 26 | 9,599 |
360 | November 27 | 9,770 |
359 | November 23 | 9,919 |
358 | November 25 | 10,001 |
357 | October 31 | 10,030 |
The late November dates are the ones that can fall on Thanksgiving, the fourth Thursday of November. Halloween just makes the list at 357th. Christmas Day has barely more than half the births of September 9.
The rarest birthdays that are not holidays
Take out Christmas, New Year, July 4, Thanksgiving week and Halloween, and a different set of dates rises to the bottom.
Rank | Birthday | Average births per year |
|---|---|---|
353 | April 1 | 10,335 |
351 | April 13 | 10,416 |
350 | May 26 | 10,425 |
346 | January 15 | 10,589 |
345 | January 29 | 10,611 |
344 | February 13 | 10,647 |
April 1 is the rarest of these. Several of the others are the 13th of a month, which fits a pattern in the full data set, covered further down. May 26 can fall on Memorial Day, the last Monday of May.
What about February 29?
Leap day is the rarest birthday by a long way, because it only exists in leap years. In the years it happened, it averaged 10,512 births, which would put it around 347th on its own. Spread over four years, that is roughly a quarter of an ordinary day's births. The odds of being born on February 29 are about 1 in 1,461. Our guide to leap year birthdays covers how leaplings count their age.
The most common birthday in each month
Every month has a busiest and a quietest date. The overall rank, out of 366, is in brackets.
Month | Most common | Least common |
|---|---|---|
January | January 24 (200th) | January 1 (365th) |
February | February 14 (62nd) | February 13 (344th) |
March | March 21 (149th) | March 13 (337th) |
April | April 4 (143rd) | April 1 (353rd) |
May | May 23 (89th) | May 26 (350th) |
June | June 27 (71st) | June 8 (210th) |
July | July 7 (7th) | July 4 (363rd) |
August | August 8 (15th) | August 3 (116th) |
September | September 9 (1st) | September 1 (255th) |
October | October 1 (47th) | October 31 (357th) |
November | November 21 (76th) | November 27 (360th) |
December | December 20 (11th) | December 25 (366th) |
Valentine's Day is the busiest date in February, and the day before it is the quietest. Even the least common day in September, the 1st, ranks above many dates in spring.
Why is September so busy?
Count back about nine months from mid-September and you land in mid to late December. Babies born on September 9 were, on average, conceived around the holiday season.
By month, September has the most births per day:
Month | Average births per day |
|---|---|
September | 11,811 |
August | 11,712 |
July | 11,563 |
June | 11,306 |
October | 11,204 |
January | 10,721 |
January has the fewest births per day of any month. That is partly the New Year holiday effect on the first two days.
Why are holidays so rare?
Doctors and hospitals avoid scheduling planned births on major holidays. Many US births are induced or delivered by planned cesarean section, and those dates can be moved by a day or two. That is why Christmas Eve, Christmas Day, New Year's Day and July 4 sit at the bottom.
The same effect shows up in the days of the week:
Day | Average births |
|---|---|
Tuesday | 12,842 |
Wednesday | 12,621 |
Thursday | 12,552 |
Friday | 12,349 |
Monday | 11,607 |
Saturday | 8,622 |
Sunday | 7,635 |
Scheduled births happen on weekdays, so a Sunday has about 40% fewer births than a Tuesday.
There is even a small dip on the 13th of the month. The 13th averaged 10,942 births, while the 6th and 20th averaged 11,259. On Friday the 13th the gap is larger: 11,744, against 12,545 for other Fridays that fall on the 6th or 20th.
How rare is your birthday?
Find your date in the tables above, or compare your date's average with 11,175, the overall daily figure. If yours is above it, you share your birthday with more people than usual. If it is below, yours is rarer. A few dates people often ask about:
Birthday | Rank out of 366 |
|---|---|
August 8 | 15th |
February 14 | 62nd |
September 11 | 91st |
March 17 | 171st |
May 1 | 220th |
January 15 | 346th |
April 1 | 353rd |
To see how long until your next birthday, try the Birthday Countdown. For your exact age on any date, use the Age Calculator.
What is the most common birthday?
September 9. From 1994 to 2014 it averaged 12,344 US births a year, the highest of any date.
What is the rarest birthday?
February 29, since it only happens in leap years. Among dates that happen every year, December 25 is the rarest.
What is the least common birthday that is not a holiday?
April 1, ranked 353rd of 366 dates, followed by April 13 and May 26.
What is the most common birth month?
September has the most births per day, followed by August and July.
Why are so many people born in September?
Babies born in September were mostly conceived in December, around the holidays.
Why are so few babies born on Christmas?
Hospitals avoid scheduling inductions and planned cesareans on holidays, so births that can be moved happen on nearby days.
Which day of the week has the most births?
Tuesday, with an average of 12,842. Sunday has the fewest, at 7,635.
Does this data apply outside the US?
The numbers are US only. Other countries show similar holiday dips, but the exact ranking differs.
Sources
US births 1994-2003 (CDC/NCHS) and 2000-2014 (SSA), FiveThirtyEight data on GitHub (all counts, ranks and averages in this post, calculated by Age Finder)
Why September 9 is the most common birthday, Popular Science (conception timing, holiday scheduling)
Leap year babies celebrate a rare birthday, Boston University, 2024 (1 in 1,461 odds)
