9th of September, birth According to data, September 9 is the most common birthday in the United States, and September is the busiest month for births overall. Several data sets have been presented that show which days and months are the most prevalent for births. They all agree on September 9 being highest. The next highest day is January 1st. September 9 is also the most common birthday in Canada and most countries around the world. It is also called "birthday season" or "birthday month". Americans celebrate their birthdays during a period from August 31 to September 10. The first day of this "birthday season" was established in 1931 by the American Association of Motor Vehicle Administrators as an official car license renewal date. Before then, cars were licensed in March for use that year, but not before then. So they created a day in between so cars would still be licensed even if someone died in a crash before or after this "renewal date." Today is the 9th of September 2019 and the fact that it is a weekday only increases its popularity: according to statistics, there are about 730 babies born on Saturdays, while only 70 are born on Sundays. Thus, the number of births on Saturday is about 8% higher than on Sunday. Moreover, there are more births on Wednesday and Thursday than on other days of the week.