The Most (And Least) Common Birthdays & Birth Months

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Plus, the reasons why birth rates have seasonal changes

Co-authored by Kyle Thomas and Dan Hickey

Last Updated: June 17, 2026 Fact Checked

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Most Common Birthdays

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Most Common Birth Month

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Most Common Zodiac Sign

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Reasons for Seasonal Births

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Least Common Birthdays

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It’s always a fun surprise when you realize someone you know shares your birthday, but did you know that some birthdays are more common than others? If you love statistics like that, then this article is for you! We’ve compiled the most common and least common birth dates (as well as the most common birth months and zodiac signs) to find out if the summer baby boom is actually real. We’ll also explore the reasons for seasonal birth rate changes to explore the why behind these fascinating stats.

Keep in mind that this data can change from year to year or country to country; the most common birthday, birth month, or zodiac sign can change depending on when and where you’re looking!

Most & Least Common Birthdays

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A chart ranking all birthdays of the year by how common they are.

September 9 is the most common birthday, while February 29 (Leap Day) is the least common birthday. Most years, about 9 of the top 10 birth dates occur in mid-September, and the majority of live births happen from July to October. Shorter, colder months with winter holidays have the least amount of births.

Section 1 of 5:

What are the most common birthdays?

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The most common birthday worldwide is September 9. While the exact date may change from year to year or from country to country, nearly all of the top 10 most common birthdays happen during a 2-week stretch in mid-September! Data collectors believe this is because couples are more likely to conceive during cold months and holiday celebrations in winter (if you count back 40 weeks from September 9, you land right between Thanksgiving and Christmas).^{[1]
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Research source} Here are the top 15 most common birthdays:
- September 9
- September 19
- September 12
- September 17
- September 10
- July 7
- September 20
- September 15
- September 16
- September 18
- December 20
- September 26
- September 8
- September 23
- December 29

Section 2 of 5:

What is the most common birth month?

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The most common birth month is August. September might dominate the list of most common birthdays, but August has the highest total of recorded live births of any month.^{[2]
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Research source} The most births typically happen between July and October (with the exact most common month changing from time to time), for the similar reason that couples are more likely to conceive during colder months.^{[3]
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Research source} September usually ranks 3rd or 4th since it only has 30 days, compared to other months with 31. Here are the most common birth months, ranked from most to least births:^{[4]
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Research source}
- August
- July
- October
- September
- May
- December
- March
- June
- January
- November
- April
- February

Section 3 of 5:

What is the most common zodiac sign?

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Virgo is the most common zodiac sign. According to astrologer Kyle Thomas, “Virgo is the most common zodiac sign, with birthdays between August 23 and September 22. The rarest zodiac sign is Aquarius. This is according to birth rate data from the United States and worldwide, [since] the month of February is the least common birth month.”^{[5]
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Expert Source

Kyle Thomas
Astrologer

Expert Interview} As you might guess, the popularity of zodiac signs generally maps onto the list of most common birth months. Here are all 12 signs, ranked from most to least common:
- Virgo (August 23 to September 22); sometimes Cancer, Leo, or Scorpio
- Cancer (June 21 to July 22)
- Leo (July 23 to August 22)
- Libra (September 23 to October 22)
- Gemini (May 21 to June 20)
- Scorpio (October 23 to November 21)
- Taurus (April 20 to May 20)
- Sagittarius (November 22 to December 21)
- Pisces (February 19 to March 20)
- Aries (March 21 to April 19)
- Capricorn (December 22 to January 19)
- Aquarius (January 20 to February 18); sometimes Capricorn or Aries

Section 4 of 5:

Reasons for Seasonal Birth Trends

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Humans tend to conceive more often during the cold and dark months. Fall and winter conception leads to the baby boom that happens in the late summer and early fall. It makes sense when you think about it—when it’s freezing cold and dark by 5pm, most couples are staying indoors for longer periods and have more time to…entertain themselves.^{[6]
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Research source}
- Plus, there are lots of holidays in the winter. This means more celebrating, more time off from work, and more relaxation (which can contribute to more conceptions).
- The opposite pattern is true in the southern hemisphere, where the seasons are flipped.
- However, as humans become more and more removed from the seasons and natural environment due to indoor work and artificial lighting, this pattern is starting to weaken. Intentional family planning contributes to this change, too.
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Male and female fertility may be higher in the fall and winter months. Some research shows that sperm quality is higher in colder weather (including quantity and mobility), whereas warm weather can make sperm more likely to be defective.^{[7]
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Research source} Female fertility is fairly stable year-round, but some evidence suggests that the shorter days of fall and winter increase your melatonin production, which can indirectly support reproductive hormones and ovulation in women (although more research is needed to confirm how much of an effect this really has).^{[8]
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Research source}
- For those seeking IVF treatment, many fertility clinics close for the holidays and schedule embryo transfers or egg retrievals in the new year, often leading to August or September birthdays.^{[9]
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  Research source}
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It’s generally more convenient to have a baby in warmer weather. Family planning makes it easier to time when you have a baby. For many families, bringing home a newborn in the summer or early fall is a lot easier than during the dark of winter! Not only is the weather milder and less stressful, but there are also fewer big holidays and commitments during the summer.
- Seasonal work may have an effect, too. For example, some teachers may time their births for the summer since they’re already off work (and do not have to be in the classroom during the most difficult months of their pregnancy).
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Some parents want their children to be slightly older than their school peers. If you were born in September, you were probably old for your class grade (since many school districts use September 1 as a cutoff for enrollment). Studies show that students who are older than their peers generally perform better academically, are slightly more likely to attend college, and exhibit other social and developmental benefits over those who are on the young end of their grade (like those with July or August birthdays).^{[10]
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Research source}
- Some parents may plan for a fall birth so that their child can enroll in school at an older age and reap the benefits of being developmentally slightly ahead of their peers.

Section 5 of 5:

What are the least common birthdays?

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The least common birthday is February 29. You’re probably not surprised that Leap Year birthdays are the least common since they only happen once every 4 years! Birthdays in shorter months and winter months are also less common than in longer, warmer months. Holiday births are also rarer as well, since most hospitals don’t induce labor or schedule C-sections on holiday dates.^{[11]
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Research source} Here are the top 15 least common birthdays ranked from least to most common:
- February 29
- December 25
- January 1
- December 24
- July 4
- January 2
- December 26
- November 27
- November 23
- November 25
- October 31
- November 24
- November 26
- November 28
- April 1