Does September 9 have the most births every year?

No. September 9 had the most recorded births in 2 of the 15 years from 2000 through 2014: 2004 and 2009. Its annual rank ranged from 1 to 306.

This study uses only the Social Security Administration (SSA) series. Across those same years, September 12 leads the combined ranking, while September 9 ranks 13. Our main birthday ranking covers a different window, combining CDC/NCHS 1994 through 1999 with SSA 2000 through 2014; September 9 leads that longer collection.

Which birthday won each year?

The table compares actual dates within each complete year. A lower rank means more recorded births; rank 1 is the year's winner. Counts describe historical U.S. birth records, not everyone alive today who shares that birthday.

September 12 leads the combined SSA series but wins only 1 individual year. September dates win 7 of the 15 years.

Counts also show how close a ranking can be. In 2010, September 9 ranked 3, with 14,135 births, just 120 fewer than that year's winner. The counts show how little separates those positions.

What changes when September 9 falls on a weekend?

Birth counts differ substantially by weekday in this dataset, as our weekday and weekend comparison shows. September 9 moves through those weekdays from year to year. For example, it fell on Sunday in 2001 and ranked 306 by births that year.

We also compare each date with other occurrences of its weekday in the same year. For this check, we divide each date's births by the average for its weekday in the same year. A ratio above one means more births than that year's average Monday, Tuesday, or other matching weekday. We then rank those ratios.

Under this different measure, September 9 in 2001 ranks 24. The table shows both rankings. The second ranks each date's ratio to the average for its weekday; the original birth counts stay the same.

Across the whole study, averaging those yearly ratios puts September 10 first and September 9 2. This measure gives a different answer from raw birth counts. It cannot tell us what caused the differences. Holiday timing and seasonal patterns remain in the data, along with other influences this calculation does not account for.

How we calculated the rankings

We used the SSA daily birth file preserved by FiveThirtyEight, covering 62,187,024 recorded births across 5,479 dates from 2000 through 2014. We use one source series throughout so that a change of source does not enter the annual comparison.

Within each year, rank equals one plus the number of dates with more births. Ties share a rank, and we retain every tied winner. February 29 participates only in leap years; an absent leap day is not counted as a day with zero births.

The combined ranking adds up the births on each month and day across the study. We also checked births per actual occurrence to account for February 29's fewer appearances; September 12 leads that measure too. For the weekday comparison across the whole study, we average each date's yearly ratios across its actual occurrences. Leap day has fewer observations here too.

Download the calculated results to inspect the annual winners, top tens, and weekday comparisons. The records end in 2014. They cannot tell us which birthday leads now or predict the busiest date in a future year. Read the full methodology for source coverage and ranking definitions, or check your birthday against the site's longer historical collection.