How Common Is Your Birthday? The following table shows every day of the year, from Jan. 1 to Dec. 31, along with a ranking based on how many babies were born in the United States on that date between 1973 and 1999. Jan. 1, for example, was the 364th most popular birthday for a baby during those years; only Dec. 25 and Feb. 29 were less popular. Sept. 16 was the most popular birthday.