September 11 is a relatively common birthday in these historical U.S. records. It ranks #91 of 366 birthday dates, where #1 means the most births. It is less common than several of the September dates around it, but it is far from the bottom of the all-year ranking.
The date had 242,785 recorded births from 1994 through 2014: 0.283% of the sample, or about 1 in 353 recorded births. That describes the selected historical records, not everyone alive with a September 11 birthday.
September 11, beside other birthdays
Average recorded births each time a date occurred, 1994 through 2014.
- Commonness rank
- 91 / 366
- Share of recorded births
- 0.283 %
- Recorded births
- 242,785
Bars start at zero. Rank 1 means most common and uses total births across all 366 dates. The bars use births per actual occurrence; February 29 appeared five times, while the other dates appeared 21 times.
Check September 11 and compare with a friend →Why can it look rare beside other September dates?
September 9, September 10 and September 12 are among the year's highest-total dates in this dataset. A date can have fewer births than those neighbors while remaining relatively common overall. December 25 is included below to show how far September 11 is from one of the lowest-total dates.
| Date | Recorded births | Commonness rank | Birth share |
|---|---|---|---|
| September 9 | 259,228 | 1 | 0.302% |
| September 10 | 255,991 | 5 | 0.299% |
| September 11 | 242,785 | 91 | 0.283% |
| September 12 | 257,913 | 3 | 0.301% |
| September 16 | 254,393 | 9 | 0.297% |
| December 25 | 138,628 | 365 | 0.162% |
Every September date occurred 21 times in the selected period. September 11 averaged 11,561.2 recorded births per actual occurrence. That is a historical average for this date, not a count of babies born on September 11 this year.
The September guide ranks the whole month. The most-common-birthday guide explains September 9's position at the top of the all-year list.
What happens when we compare the same weekday?
Adjacent dates fall on different weekdays in each year. Since weekday and weekend birth counts differ, an adjacent-date comparison can mix a date pattern with a weekday pattern.
We also use SSA records from 2000 through 2014 and compare each September 11 with the average of the dates one and two weeks before and after it in the same year. Those comparison dates share its weekday. Across this separate window, September 11 had 3.2% fewer births than the combined comparison average. It was lower in 9 years and higher in 6.
| Year | Weekday | Recorded births | Nearby mean | Difference |
|---|---|---|---|---|
| 2000 | Monday | 12,405 | 11,415.8 | +8.7% |
| 2001 | Tuesday | 13,590 | 13,470.5 | +0.9% |
| 2002 | Wednesday | 12,655 | 13,709.5 | -7.7% |
| 2003 | Thursday | 13,196 | 14,047.8 | -6.1% |
| 2004 | Saturday | 9,253 | 9,114.8 | +1.5% |
| 2005 | Sunday | 8,041 | 7,991 | +0.6% |
| 2006 | Monday | 12,868 | 12,357.3 | +4.1% |
| 2007 | Tuesday | 14,063 | 14,635.3 | -3.9% |
| 2008 | Thursday | 13,391 | 14,596.5 | -8.3% |
| 2009 | Friday | 13,032 | 13,638 | -4.4% |
| 2010 | Saturday | 8,775 | 8,681.5 | +1.1% |
| 2011 | Sunday | 7,501 | 7,591.3 | -1.2% |
| 2012 | Tuesday | 12,543 | 13,444 | -6.7% |
| 2013 | Wednesday | 12,074 | 13,273.3 | -9.0% |
| 2014 | Thursday | 12,104 | 13,333.3 | -9.2% |
September 11 falls below the nearby-weekday average across the full window, but not in every year. Matching weekdays does not remove every seasonal or holiday difference, and it does not explain any family's delivery timing.
Does this show that the 2001 attacks changed birth timing?
The pooled rank does not answer that question. It combines births before and after 2001, and the yearly comparison is not a study designed to isolate the attacks' effect.
A change in raw counts could also reflect changes in the total number of births, weekday patterns or source coverage. September 11 has fewer recorded births than several very common September neighbors. Across the full year, it remains a relatively common birthday in this sample.
Sources and calculations
The counts come from daily U.S. birth files compiled by FiveThirtyEight, using CDC/NCHS for 1994 through 1999 and SSA for 2000 through 2014. We exclude the overlapping CDC years. The sources have different administrative coverage; the yearly weekday comparison uses SSA alone.
Birth share divides September 11's count by all births in the selected records. Rank compares totals across 366 month/day combinations. See the methodology for source selection and definitions, or use the birthday checker to compare September 11 with another date.
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