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 the number of people born on each day of the year between 1973 and 1999, results showed that the most common birthday for U.S. residents was September 16, followed by September 9, 23, 17, 22, and 21. Newer averages from the U.S. Social Security Administration show that between 2000 and 2014 the day with the largest number of births has become September 9, followed by September 19, 12, 17, and 10, and then July 7. The rest of the top 10 most common birthdays are in September, the most common birthday month.
The least common birthday month is January. The Social Security averages show 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 everywhere, but results showed that the farther north the birthplace, the earlier in the summer the birthday; thus June 27 in Massachusetts, and more births in October in equatorial countries.
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
No study has confirmed the most common zodiac signs. This is because births during "cusp" periods -- from the 19th to 23rd of any month -- require precise birth times to pinpoint the placement of the Sun as it leaves one zodiac sign and travels into the next.
But from available evidence we can figure that the most common zodiac Sun signs are 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.
If you have plenty of Leo, Cancer, and Scorpio friends, that is natural, because they were born in one of the four most popular birth months. Those born in the first three weeks of July are Cancers; late July and early August children are Leos. Those born in the first weeks of October are Librans, and those born in the last ten days of October are Scorpios.
Working backward from this information we see that late-summer early-fall birthday people were conceived in late fall to mid-winter, with conceptions peaking around Christmas and New Year's Day. An online claim that Scorpio (October-November) is the most common zodiac sign, followed by Virgo and then Gemini, gives no source for that information. But as Valentine's Day, February 14, has been inflated into a major U.S. holiday, there are more November births, peaking on the days November 1, 7, 19, 20 and 21. The millennial generation seems to include a larger percentage of Scorpios.
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. 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?
© 2011 SylviaSky