Sept. 30 is the Netherlands' most common birthday, tied to holiday-season conceptions

More people in the Netherlands celebrate a birthday at the end of September than on any other stretch of the calendar, with September 30 ranked as the single busiest date. On that day, at least 44,034 people celebrate their birthdays. According to Statistics Netherlands (CBS), demographers link the pattern to conception around the winter holidays.

September 20, 21, 23, 24, 25, 28, and 29 are also among the 10 most common birthdays. July follows as the next busiest month. The statistics agency added that someone has a birthday on virtually every date in nearly every Dutch municipality.

January, November, and December have the fewest birthdays. February 29 is the rarest date of all, with 9,609 people born. That is mainly because the date occurs only in leap years. Apart from the leap dates, January 1 is the least common birthday, with 31,579 people born.

The seasonal patterns have shifted over generations. Younger residents are more likely to have September birthdays, CBS analyses show. People aged 75 and older more often were born in spring. Births that were once concentrated in spring now tilt toward late summer.