Why January birthdays dominate sports but mean nothing in esports — a study of 15,000 pros upends 40 years of sports science

Look closely at the rosters of Canada's national ice hockey team, elite youth soccer academies across Europe, or even the world's top chess players, and a curious pattern emerges: a disproportionate number were born early in the year.

The reason lies in how young athletes are grouped by age for competition. A child born in January and one born in December are placed in the same cohort, yet the January child has had nearly a full extra year to grow. The bigger, faster kid gets labeled "talented," gets picked first, and receives better coaching and more playing time.

It is the "relative age effect" (RAE) — a phenomenon confirmed in sports science for more than 40 years.

But does a birthday also determine success in esports, where players compete with their fingertips and minds rather than their bodies? An analysis of more than 15,000 professional gamers suggests the answer is no.

In the July 2026 issue of the international journal Frontiers in Psychology, Kang Ji-moon, a professor at Korea University's School of Media, published findings from an analysis of the birth dates of 15,065 professional players from 177 countries across 609 titles, drawn from Esports Earnings, a global esports prize-money database.

Monthly birth distribution of professional esports players. Blue bars represent birth counts; the orange line shows expected birth counts based on average monthly birth rates in the United States and South Korea. [Frontiers in Psychology, July 2026]

Birth month had no bearing on turning pro in esports

The bottom line: there was no relative age effect in esports. Players born in any quarter of the year turned professional at roughly equal rates.

At first glance, the raw numbers seemed to point the other way — early-year births were the least common among pros, while summer and autumn births were the most common. More people are simply born in summer to begin with; in the Northern Hemisphere, births cluster between July and September. Once the data were adjusted for actual monthly birth rates, the differences disappeared.

Kang cross-checked the findings against each country's school-year cutoff date for further confirmation. The cutoff varies — January in South Korea, September in the United States and China, April in Japan. If the RAE were real, the same birthday should yield different outcomes depending on the country.

The correlation between cutoff date and player performance was in effect zero. Among the 1,216 South Korean players in the dataset, simply shifting the reference point from March to January flipped which birthdays were "advantageous" to the opposite end of the calendar — confirming the absence of a relative age effect.

Player survival curves by birth quarter. Curves for the first through fourth quarters overlap almost entirely. [Frontiers in Psychology, July 2026]

Debut age was the real variable

Even after turning professional, birth month did not translate into a longer career or higher earnings.

Career survival curves for early-year and late-year players were nearly identical. Matched-pair comparisons of prize winnings between players with similar profiles showed no meaningful gap.

What shaped a professional career was not birthday but debut age. Each additional year of delay in turning pro was associated with roughly 18 percent lower career prize earnings and a nearly 10 percent higher risk of retirement.

Players born later in the year debuted on average about two months earlier, which translated into a marginal edge in total earnings.

Several factors explain why the RAE does not apply in esports.

Gaming performance generally comes down to reaction speed and decision-making — areas where a few extra months of physical growth offer no advantage. There is also no age-grouped youth selection pipeline to filter players out. Online ranking systems allow anyone to break into the professional scene on skill alone.

Esports organization T1's League of Legends roster with Nvidia CEO Jensen Huang. (Yoon Chang-bin)

Youth academy systems could bring the relative age effect to esports too

Among the youngest cohort — those born after 2006 — the same pattern seen in traditional sports did appear. Players born early in the year outnumbered those born late in the year by roughly 1.9 to one.

The average debut age for this group was 15.7, a period that coincides with esports organizations beginning to establish youth academies and age-restricted leagues.

The implication is that esports, as it professionalizes and formalizes, is starting to replicate the very birthday bias that traditional sports have spent the past 40 years trying to overcome.

In the paper, Kang called this risk the "paradox of institutionalization" — the idea that the fair, open competition online play once provided could narrow as formal youth systems and academies expand, allowing the relative age effect that traditional sports have long identified as a problem to seep into esports as well.

Kang said preemptive corrective measures are needed before the pattern becomes entrenched. Building mechanisms into the selection process that account for developmental differences tied to birth date, he argued, is the only way to prevent talented teenage prospects from being pushed out early simply because they were born later in the year.

Kang noted, however, that the sample for this youngest cohort was still limited at 449 players, and that only about 10 percent of all players in the database had publicly available birth dates — constraints he acknowledged as limitations of the study.

Reference

DOI: 10.3389/fpsyg.2026.1829930

Kang J (2026) No relative age effect in professional esports: a cross-national test of selection mechanisms. Front. Psychol. 17:1829930.

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