August is the most common birth month by total births. September is the most common by births per day. February is the least common birth month by total births. January has the lowest births per day.
85,712,738 U.S. births. 1994–2014 · CDC/NCHS + SSA. Sources & method
What are the most and least common birth months?
The answer depends on the measure. Total births count all recorded births in a month. The daily average divides that total by the month's covered calendar days.
- Most common by total births: August, with 7,624,626 births, or 8.9% of all births.
- Most common by daily average: September, with about 11,810.6 births per day.
- Least common, or rarest, by total births: February, with 6,511,697 births, or 7.6% of all births.
- Least common by daily average: January, with about 10,720.9 births per day.
February has the fewest covered days. By daily average, it ranks #8 of 12. Its shorter length helps explain its small total.
September has the highest daily average.
Daily averages account for differences in month length. February’s day count includes leap days.
| MONTH | RECORDED BIRTHS | SHARE | COVERED DAYS | DAILY AVERAGE |
|---|---|---|---|---|
| January | 6,979,322 | 8.14% | 651 | 10,721 |
| February | 6,511,697 | 7.60% | 593 | 10,981 |
| March | 7,147,368 | 8.34% | 651 | 10,979 |
| April | 6,850,733 | 7.99% | 630 | 10,874 |
| May | 7,175,367 | 8.37% | 651 | 11,022 |
| June | 7,122,586 | 8.31% | 630 | 11,306 |
| July | 7,527,284 | 8.78% | 651 | 11,563 |
| August | 7,624,626 | 8.90% | 651 | 11,712 |
| September | 7,440,659 | 8.68% | 630 | 11,811 |
| October | 7,293,822 | 8.51% | 651 | 11,204 |
| November | 6,884,173 | 8.03% | 630 | 10,927 |
| December | 7,155,101 | 8.35% | 651 | 10,991 |
Historical U.S. birth records, 1994–2014. Read about month-length adjustments.
Two measures, two leading months
These charts keep all twelve months in calendar order. The first compares total recorded births. The second divides each total by its actual covered days.
Download the full-size month comparison or read the pinned source data. The table above gives the values and covered days for every month.
Does adjusting for month length change the most common birth month?
August has the most total births, while September has the highest average per calendar day in the U.S. records from 1994 through 2014. Dividing by the number of days changes which month comes first.
August contains 7,624,626 births across 651 covered days. September contains 7,440,659 across 630 days. August gets one extra day each year, giving it 21 more days in this dataset.
| Month | Recorded births | Covered days | Births per day |
|---|---|---|---|
| August | 7,624,626 | 651 | 11,712.2 |
| September | 7,440,659 | 630 | 11,810.6 |
| February | 6,511,697 | 593 | 10,980.9 |
How to compare a 30-day month with a 31-day month
For the daily average, divide a month's total births by all its actual calendar days in the coverage period:
Average births per day = total births in the month ÷ covered calendar days
For September, 7,440,659 ÷ 630 gives about 11,810.6 births per day. August's average is about 11,712.2. September's daily average is 0.8% higher, even though its total is smaller.
Totals tell you which month contains the most recorded birthdays. Daily averages tell you which month has the most births per day. You can switch between the two in the chart above.
Is February still the least common birth month?
February has the fewest total births in these records, at 6,511,697. Its 593 covered days include all five February 29 dates in the period.
After dividing by those days, February averages 10,980.9 births per day. It ranks #8 of 12 by daily average, where #1 means the highest average. January has the lowest daily average, at 10,720.9.
February's shorter length helps explain its small share of annual births, even though its daily average is higher than January's. February 29 needs a similar adjustment when you compare individual dates.
What the adjustment can tell you
Daily averages remove the difference in the number of calendar days. They still reflect the years, weekdays, and holidays in the records. They do not establish why births follow a seasonal pattern or predict the most common month in a different country or year.
For another calendar comparison, see births on weekdays and weekends. To look up an individual date, use the birthday checker or full birthday ranking.
Sources for the month comparison
All values come from FiveThirtyEight's historical U.S. birth files, using CDC/NCHS for 1994 through 1999 and SSA for 2000 through 2014. See how we count months for the denominator and source details. We use actual covered dates, including leap days, and round only the displayed results.
For individual dates, see the rarest and most common birthday in every month . Our date distribution study compares all recurring birthday dates with an even daily spread.
Where does your date rank within its month?
These guides compare every date in a month, with both month and overall ranks.
- January birthdays
- February birthdays
- March birthdays
- April birthdays
- May birthdays
- June birthdays
- July birthdays
- August birthdays
- September birthdays
- October birthdays
- November birthdays
- December birthdays