That’s why most of you celebrate your birthday at the end of September

It is very likely that you have several people in your circle whose birthdays will be celebrated in the coming days. Know that randomness has (almost) nothing to do with it. A 2011 INED report showed that since the 1970s, the number of births in France has been particularly high between the end of September and the first week of October. The calculation is simple, and the explanation is nine months earlier on New Year’s Eve.

Christmas night effect

According to the conclusions of the survey, the New Year’s Eve would be favorable for fruitful intimate relationships. The phenomenon is known to demographers as the “New Year’s Eve effect.” Generally gathered for the occasion, couples are on vacation, the atmosphere is festive, and contraceptives are often forgotten. Alcohol compels, some women also give up their pill, throwing up on the evening of the 31st. The peak of births will then be particularly noticeable on September 23, that is, exactly 265 days after the specified evening, which corresponds to the classical gestation period. .

“The Paradox of the Christmas Season”

This phenomenon is all the more surprising because it in no way reflects the preferences and birth plans of French women, according to the authors of the INED study. Indeed, a 2010 survey by one of them found that only 2% of women surveyed would choose September to give birth if given the chance. This is what they call the “Nativity Season Paradox.”

This perhaps explains the fading of this New Year effect since the study was published. According to INSEE, this peak of births in September has been less and less pronounced since 2015 (except for a setback in 2021). While the new one is expected, this time in July.