Birth month is a big factor in athletic performance

Becoming a professional athlete requires years of practice and determination. The old saying of ”no pain-no gain” certainly applies when talking about reaching your peak performance. However, there are also other factors in play which have a clear indication of future success as an athlete. One of which is to be born at the right time of the year. 

The Relative Age Effect

Most sports divide teams and leagues by calendar year, which means kids from the same league can be born anywhere between January 1st to December 31st. During this time, those who are more developed in terms of size, strength and skill will stand out on the field. A simple chronological fact is that there can be nearly a full year of physical development between two players born on the same year. This is called the Relative Age Effect and it is especially apparent among young players and adolescents. (1,2,3,4)

A cumulative effect

Especially among younger players, being physically mature is usually the first thing that gives them the edge against others players and makes them stand out. Their skill and/or maturation, along with positive feedback from parents and coaches multiply and gives the player a great deal of confidence. In short, the athlete is showing promise, which helps them get picked earlier for a next-tier team. At this point, they will get to play against better teams, better opponents and become better athletes. (1,3,4)

How physical maturity can shape athlete development
How physical maturity can shape athlete development

Basically it means that physical characteristics could determine the fate of young athletes by giving them access to better coaching and training. (4)

Psychologically speaking, the higher the child’s perceived competence is, the more likely it is for him/her to persist and participate in the sport (5).
Whether it is mastering a new skill, having fun, winning or being around a successful group of young athletes, this age requires some delicate help from the people around them. And being physically one of the most mature definitely has it’s advantages in progressing as an athlete.

In this case however, you will not receive the same sort of rejectment as you would as a physically smaller athlete. Therefore, the progress for these athletes may be hindered unless they are extremely competitive and show an ”I’ll prove them wrong” attitude.

In the worst case, without positive affirmation these individuals may want to drop out of the sport (4).

Performance without injuries

Within younger age groups, growth and maturation are major factors in success, performance and possible injury. With this in mind, the cutoff age has two important effects;

1. Relatively older children are more likely to succeed in both academics as well as sports (1).

2. Relatively older children have a lower risk of injury because of their skill, size and cognitive development (1).

Physically smaller children are more likely to sustain injuries that may hinder their development even further. However, I do believe that most of these injuries can be prevented with smart training and body maintenance.

Talent versus age

The misconception talent and age leads to think that early maturation would have something to do with the whole process of becoming an athlete. While this may have a cumulative effect, is not entirely black and white. Some of the most skilled yet physically smaller players suffer from not being able to play at a level that supports their development. However, talent and size are not synonymous.

Moreover, physical size does not always translate into better performance on the field. While certain sports seem to benefit from specific physical traits, some require rapid changes in pace and direction that could be better-suited for lighter built athletes. For example football (or soccer), shorter athletes can accelerate better, react quicker,  have a greater strength-to-weight ratio and move with more agility (6).

Birth month affects performance in ice hockey
Photo by Alan Levine

There are a number of parents and even coaches that think of size and strength as a determining factor in performance and progress. This can determine whether the player ”makes the cut” for a certain team that supports further skill acquisition. This is especially apparent in sports such as football, rugby and ice hockey where size may be seen beneficial (1,2).

Talent is ofter overlooked by coaches and teachers

Sometimes teachers and coaches mistakenly favor those who are more mature in order to select a team more likely to succeed. This means that every training session and drill could be swayed into the direction of supporting the skill sets of those who are relatively older. From a competitive standpoint this decision might be rational, but it does create a huge disadvantage for younger participants.

This can also be seen in how teachers may select older gifted individuals for academic programs because they are more likely to succeed and benefit from it (3).

Why does this happen?

This occurs simply because sports become very competitive at a very early stage and teams want players that are already at a level which benefits the team. There is hardly any room for a player to catch up. If a player peaks early by being mature but never really progresses to the next level, they will simply be dropped to another team. However, by then those same teams may have lost other highly skilled players simply because were not physically ready a year earlier.

Relative age effect is still apparent in major sports leagues

Relative Age Effect is still a very common phenomenon and it can be seen in a variety of different sports. For example, Deaner et al.  studied elite Canadian junior team players and found that 40% of the players were born on January, February or March. (3). Other studies have stated that players born during that time are four times more likely to make it in the big leagues (4).

On the adults’ side in the NHL, these statistics show similar results, although not as in a drastic manner. Here’s a little infographic of this season’s athletes and their birth months.

Analysis of athletes birth months during the 16/17 season and how it affects performance
Statistics of the birth months of NHL players on the 16/17 season

As you can see, the relative age effect is still clearly visible in the biggest ice hockey league in the world. While it is not as high as the 40% in the junior league, three out of ten (30%) NHL players are born in the first quarter of the year. The result is still remarkable and shows that birth month can indeed be an indicator of athletic ability.

Let’s not forget about soccer

The same kind of effect was also visible during the 2016 UEFA European championship tournament, where 57% of the players were born on the first half of the year. A great example of this is Cristiano Ronaldo, who led the Portuguese team to victory in the tournament (and recently got this statue made of him). He is born on the 5th of February.

Another interesting statistical find was that Northern and Central European countries had less players born during the cold months (January, February and March) compared to Mediterranean countries.

Go figure!

The bottom line

Needless to say there is still a possibility to become an athlete even if you are not lucky enough to be born at the beginning of the year. There is an long list of athletes who have had a impressive professional career despite being born after the first six months of the year. Obviously the commitment, motivation, genetics – even finances are a huge factor in whether a career in sports is possible.

There are also many aspects to this phenomenon. One might think that relatively older athletes have an access to get into better training groups, which help future skill development. However, is it possible that those physically smaller individuals, who have had to overcome the size difference time and time again, to be better because they have had an unfair advantage early on?




1. Stracciolini, A, Levey Friedman, H, Casciano, R, Howell, D, Sugimoto, D. & Micheli, Lyle J. 2016. The relative age effect on Youth Sports Injuries. Medicine in sports and exercise 48(6). p1068-1074.

2. Buchheit, M, Mendez-Villanueva, A, Mayer, N, Jullien, H, Marles, A, Bosquet, L, Maille, P, Morin, J.-B., Cazorla, G. & Lambert, P. 2013. Locomotor performance in Highly-Trained Young Soccer Players: Does Body Size Always Matter? International Journal of Sports Medicine 35(6).

3. Deaner, R.O., Lowen, A. & Cobley, S. 2013. Born at the Wrong Time: Selection Bias in the NHL Draft. PLOS ONE 8(2). p1-7.

4. Baker, J. Genes and training for Athletic Performance Revisited. 2001. School of Physical and Health Education, Queen’s University, Kingston, ON. Sportscience 5(2). 2032 words.

5. Weinberg, R., S. & Gould, D. 2015. Foundations of Sport and Exercise Psychology, 6th Edition. Human Kinetics, P.O. Box 5076, Champaign, IL. p531-547.

6. Samaras, T. 2007. Human Body Size and the Laws of Scaling: Physiological, Performance, Growth, Longevity and Ecological Ramifications, Nova Publishers, NY.

Other sources:

Analysing Birthdates of EURO 2016 Players


Leave a Reply