The Most Common and Least Common Birthdays and Zodiac Signs
What Definitive Sources Say
On the average, 11,000 babies are born in the U.S. every day. When a Harvard University study counted U.S. births each day of the year between 1973 and 1999, it found the most common birthday for U.S. residents was September 16, followed by September 9, 23, 17, 22, and 21. Between 2000 and 2014, the Social Security Administration listed the most common birthday as September 9, followed by September 19, 12, 17, and 10 -- and then a surprise: July 7.
July was a trend, and in 2014 and 2015 became the number-one U.S. birth month. Both years August was a close second, and then September. In 2013, the top three months were August, July, and October. From 2015 to 2017 the U.K.'s top three birth months were July, September, and then August. These statistics are the latest available from the United Nations, which compiles birth-month data for every member country.
The least common U.S. birthday month is February. Social Security figures showed that for the entire span of January 1 through May 22, the most popular birth date is February 14: Valentine's Day.
The Rarest Birthdays: Holidays, April 1, and Any 13th
Studies of the most common individual U.S. birth dates show they always cluster from midsummer to early autumn, with minor variations. One study by the now-defunct data site anybirthday.com found the most common birthday to be October 5, and the least common, May 22. The Harvard study gave December 25, Christmas, as the least common birthday, and January 1 and December 24 as the next least common. This reflected a trend during the study years, 1973-1999, to induce or delay childbirth for reasons of convenience.
Newer information from 2000-2014 shows that this pattern--many fewer births on holidays--is unchanged, with the top 10 least common U.S. birthdays all on major holidays or adjacent to them. December 25 is still the rarest birthday, with only about 6500 babies born that day. The next least common birthdays are January 1, December 24, July 4, January 2, December 26, November 27, November 23, November 25, and October 31.
The rarest U.S. birthdays outside of holidays are April 1 and April 13. An infographic analysis of the Social Security data shows that when U.S. parents can schedule a birth, they avoid the 13th of any month.
Birthdays and the Seasons
A study of births in Massachusetts covering 2005 to 2014 said the most common birthday in that state was, surprisingly, June 27, and the second-most-common September 19, then August 1, then July 7. Its much larger source study, originating at Princeton University, compiled 78 years of birth data including all 50 states and 118 mostly Northern Hemisphere countries. Midsummer to autumn was baby season, but results showed that the farther north the birthplace, the earlier in the summer the birthday; thus June 27 in Massachusetts. In equatorial countries birth numbers are higher in mid-spring and late autumn.
In England and Wales the least common birthdays are December 25, December 26 (Boxing Day), and January 1, and the most common, September 26. The prevalence of late summer-early autumn births is natural, according to some sources--tied into the harvest season, when food is especially plentiful.
But in New Zealand, government birth data gathered from 1980 to 2015 shows December 25 is also the least common birthday, and the most common is September 30. Christmas in New Zealand is in the summertime, so December, January and February don't have to be cold to inspire more baby-making.
Most Common and Least Common Zodiac Signs
From available evidence we can figure that the most common zodiac Sun signs for adults older than 30 would be Virgo, governing those born around August 20 until September 21, and Libra, for those born in the last week of September and first three weeks of October. A popular meme ranks Scorpio first, then Virgo, then Gemini, then Pisces, but it gives no source for that information.
The under-30 U.S. population does seem to include a larger percentage of Scorpios. During the last 30 years the February holidays Valentine's Day, Mardi Gras (80 percent of the time it's in February), and football's Super Bowl game day have all been inflated into major U.S. party days. As a result there seem to be more November births, peaking on November 1, 7, 19, 20 and 21.
For a true count, births from the 19th to 23rd of any month, on the Sun sign "cusps," must be counted year by year to pinpoint the placement of the Sun as it leaves one zodiac sign and travels into the next.
The month with the fewest birthdays is February because it's the shortest month, but the full-length month with the fewest birthdays is January, making Aquarius (late January to February 21) the least common zodiac sign. No sources agree on the second-least-common zodiac sign, although some suggest it is Gemini, and some Leo. If we were to count only the youngest Americans, the second-least-likely zodiac sign would be Capricorn.
But We Have the Same Birthday!
In a group of 70 random people the chance is 99.9 percent that two of them share a birthday. Among 200 people, the chance is 100 percent. Among only 23 people, the chance is an amazing 50 percent.
How this can be so when there are 365 different birthdays? (February 29 is excluded.) This is a brain teaser for probability theorists, who call this "The Birthday Paradox" or "The Birthday Problem."
Which Sign is Most Common?
Which Sign Do You Think is Most Common?
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2011 Sylvia Sky