What is the most common birthday?
The busiest dates are close together rather than separated by a huge gap. Several September dates sit near the top, which is why the top 10 tells a better story than a single first-place date.
The 10 most common birthdays in the historical U.S. data
The list is ordered by total recorded births for each month-and-day combination. “Common #1” is the date with the highest total; the main calculator separately reports its rarity rank among all 366 dates.
September 9
259,228 recorded births, representing about 0.302% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
September 19
257,981 recorded births, representing about 0.301% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
September 12
257,913 recorded births, representing about 0.301% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
September 17
256,231 recorded births, representing about 0.299% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
September 10
255,991 recorded births, representing about 0.299% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
September 20
255,392 recorded births, representing about 0.298% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
July 7
255,094 recorded births, representing about 0.298% of the 85,712,738 births in the source series.
This July date is one of the few non-September dates to reach the very top of the historical ranking.
September 15
254,652 recorded births, representing about 0.297% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
September 16
254,393 recorded births, representing about 0.297% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
September 18
254,350 recorded births, representing about 0.297% of the 85,712,738 births in the source series.
This date sits inside the strong September cluster visible in the historical U.S. records.
Why are so many common birthdays in September?
The observed records show a strong cluster in September, with several nearby dates among the highest totals in the entire 21-year series. The ranking reports what is in the historical data rather than adding a seasonal boost by hand.
Possible explanations for seasonal birth patterns include conception timing, holidays, weather, and medical scheduling, but this calculator does not try to assign a single cause to the pattern.
What does a common birthday mean?
A common birthday simply means that more births were recorded on that month and day than on most other dates in this historical U.S. series. It does not make the birthday less meaningful, and it says nothing about the personality or individuality of people born on that day.
For comparison, February 29 sits at the rare end of the same 366-date table. The rarest birthdays page shows those low-count dates.
Most common birthday questions
What is the most common birthday?
September 9 has the highest total in the 1994–2014 U.S. records used by this site, with 259,228 recorded births.
What is the busiest birthday season?
The highest-ranking dates cluster strongly in September in this historical U.S. dataset.
Is this the most common birthday everywhere?
Not necessarily. These rankings use U.S. records from 1994–2014. Other countries and time periods can have different patterns.
Why does a common birthday receive a low rarity score?
The score rises toward the rare end of the ranking, so dates with higher recorded totals receive lower rarity scores.