Whether you were born in December, January, August or September can have a significant and long-lasting impact on your life. Our new research shows your birthday month may also contribute to shaping your personality. In particular, we found people’s self-confidence can significantly differ because of their month of birth.
The reason isn’t your astrological sign, but rather the role your birth date plays in deciding when you enter school. Most countries specify when young children should start school using a cut-off date in the year.
For instance, in the UK the cut-off date is September 1. In federal nations such as Australia or the US, cut-off dates vary between states. Children who turn five by the cut-off date will start school, while children whose birthday is after the cut-off date will still be four and start school the following year.
The relative position of your birthday to the school cut-off date has one important consequence: it determines whether throughout primary and secondary school you are among the older, more mature, taller students in the class or not.
Relative age and career success
It’s well known that relative age at school can have a long lasting impact. A large body of research has shown, for example, students who were relatively old among their peers are more likely to become professional sports players. This pattern is evident across a wide range of sports in many different countries with different cut-off dates: soccer, ice hockey and AFL.
Famous footballers who were relatively old among their peers include for instance Pep Guardiola, the current manager of Manchester City.
Studies have also found relatively old students do better at school. Even though the advantage tends to decrease over time, they are still slightly more likely to go to university. The long term impact on professional achievement doesn’t seem very large, but in some highly competitive environments, people who were relatively old at school are substantially over-represented.
This is the case among CEOs of large corporations. Previous research found this was also the case among leading US politicians.
The role of self-confidence
Our research suggests one of the main reasons for this “birthday effect” is the impact of relative age on self-confidence. Recent research shows children who enjoy being ranked relatively high compared to their peers have higher self-confidence. Being relatively old among your peers tends to place you higher in the distribution of achievement. Children who enjoy this throughout childhood can end up being more confident in their aptitude and carry this confidence with them later on.
To test this idea, we conducted two studies. The first was with Australian school children in years eight to nine (13- to 15-year-olds) born one month apart from the school cut-off date.