The most common month overall for birthdays is September followed closely by August and July. Specifically, September 16th is the most common birthday in the United States. According to the Centers for Disease Control, however, the most common month for births over the past several years has been August.
The most common birth months correspond to conception taking place during the holiday season as well as during winter, suggesting that both festive moods and winter blahs may be responsible for the majority of births. The month with the least amount of births January, suggesting that late spring is not traditionally a time when people are focused on starting or expanding a family.