What is the Relative Age Effect?
In football, age groups are determined by calendar year. Someone born in January plays in the same age cohort as someone born in December – even though there can be up to 11 months' age difference between them.
For a 9-year-old January child and an 8-year-and-1-month-old December child, the age difference represents over 10% of their lifespan so far. At that age, it is an enormous advantage.
Consequence: The older players in an age group are physically stronger, more coordinated, and cognitively more advanced. Coaches select them more frequently. They receive more playing time, more coaching, and greater confidence. They develop faster – not because they are more talented, but because they were nurtured earlier.
Compounded over years: The advantage grows rather than shrinks. A player favoured at U11 is stronger at U13, noticeably superior at U15, and selected for elite development pathways at U19 – even though the initial advantage was merely a few months of life experience.
The data behind it
Studies clearly demonstrate the effect:
- In German NLZ academies (Nachwuchsleistungszentren), players born from January to March feature roughly 2 to 3 times more often than those born from October to December
- In professional Bundesliga squads: a similar distribution
- In DFB representative teams: an even stronger effect
This is not a random distribution. It is systematic bias.
Why the RAE exists
Three interconnected causes:
Cause 1: Physical maturity
A 9-year-old boy born in January is, on average, 3–5 cm taller than an 8-year-and-1-month-old boy born in December. In physical duels, aerial challenges, and sprints, he holds an edge.
Cause 2: Cognitive maturity
Game understanding, concentration span, learning from mistakes – all of these depend on maturity level. Older children in an age cohort grasp instructions faster and make better decisions.
Cause 3: Confidence and experience
Older children have more life experience. Greater confidence. They back themselves more. They command a stronger presence in training sessions and matches.
Why the RAE is a problem
Four major consequences:
Consequence 1: Genuine talent is overlooked
A highly gifted December child gets overlooked because they appear weaker in direct comparison with an average January child. Talent is not discovered; it is filtered out.
Consequence 2: Injustice for the children
A child who misses out on a development pathway often stops playing football with serious ambition. That talent is then lost forever.
Consequence 3: Distortion of the player pool
At the highest level, players who were filtered out due to the RAE are missing. German football loses overall quality across the board.
Consequence 4: Self-reinforcing cycle
Those who receive early support improve. Those who do not fall behind. Over the years, that initial difference in birth month turns into a massive performance gap.
What you can do specifically as a youth coach
Six actionable strategies:
Strategy 1: Assessment in context
When assessing players (in Coach OS or on paper), make a conscious note of their birth month. A player rated 6/10 born in December may well become an 8/10 in a year's time.
Tip: In Coach OS, you can record the birth month in the player profile. Keep it visible during assessments so you avoid making false comparisons.
Strategy 2: Actively balance playing time
Late-born players often get less playing time. You can actively counteract this: give December-born players just as many minutes on the pitch as January-born players.
When planning your line-up and distributing minutes, consciously track birth-month distribution.
Strategy 3: Organise 1v1s by maturity stage
In game formats, you can deliberately match players based on physical maturity. Instead of merely matching "talent against talent", also pair "older child against older child" and "younger against younger".
This gives younger players in the age cohort fair conditions to show what they can do.
Strategy 4: Multiple assessment points
If you only assess once per season, you will miss how players are developing. With three assessments per season (the Coach OS standard), you can track development velocity – and identify December-born players who are catching up rapidly.
Strategy 5: Recommendations for higher levels with an RAE note
When recommending a player to an academy or a scouting trial, include a note: "Born in December, above-average development over the last 12 months." This provides the scout with crucial context.
Strategy 6: Educate parents
Parents often do not understand the RAE. "My child just isn't as good as Tim." You can explain: "Tim is 10 months older. At this age, that is a massive difference."
This removes unnecessary pressure from the relationship with parents.
What clubs can do
At club level, there are further options:
Measure 1: Bio-banding
Group players by biological maturity rather than calendar year. In the professional game (e.g. at Manchester City), this is already practised: players are temporarily assigned to maturity brackets rather than standard age groups.
Harder to implement in grassroots football, but entirely feasible for specific phases in training sessions.
Measure 2: Keep an eye on late bloomers
Clubs should actively search for late bloomers. A player who does not yet have the maturity of a 13-year-old at age 14 can turn out to be an outstanding player at 17.
Through the Coach OS club dashboard, the head of youth development can keep these players on the radar.
Measure 3: Multiple teams, fluid transitions
If a club runs two teams per age group, players should be able to move between them depending on their development. This ensures nobody is locked into a fixed tier for an entire season.
Measure 4: Parent education as a club initiative
Host parent meetings on the topic "Why your child might not be in the top development team" – accompanied by an explanation of the RAE.
What you should NOT do
Mistake 1: Denying the effect
"At our club, children play regardless of their birth month." Statistically, that is almost certainly untrue. You are not immune to RAE effects either – you simply have to recognise them.
Mistake 2: Devaluing older children in the age cohort
This is not about putting January children at a disadvantage. It is about establishing fair conditions for everyone.
Mistake 3: Turning December children into heroes
Avoid this as well. They are not "better because they are disadvantaged". They simply deserve the same opportunities.
Mistake 4: Treating the issue as solved
The RAE has been documented for decades, yet has barely diminished. It remains an unresolved challenge.
How to recognise the effect in yourself
Three self-tests:
Test 1: Birth months of your starting XI
Write down the birth months of your regular starting line-up. If 70–80% fall into the first half of the year: you have an RAE bias.
Test 2: Who gets substituted?
Check the playing-time statistics from your last 10 matches. Who is frequently brought on, and who gets taken off? If a pattern by birth month emerges: RAE.
Test 3: Who was recommended for higher teams?
If all your recommendations are players born between January and March: RAE.
If any of these tests come back positive, you need to take action. If all are positive, you are part of the system – without intending to be.
How the RAE is addressed in professional football
At Bayern, the DFB, and across the Bundesliga, the RAE has been a talking point for years. Several professional clubs run deliberate initiatives:
- TSG Hoffenheim has actively factored in birth months in talent development to balance things out
- Manchester City experiments with bio-banding
- DFB base development centres (Stützpunkt-Programm) are increasingly run with RAE awareness
However: the effect is stubborn. Without active countermeasures, it persists.
How Coach OS helps you with RAE awareness
Coach OS documents birth months in player profiles. You can:
- View the birth-month distribution of your starting XI
- Track player rating trends in the context of their birth month
- Filter playing-time statistics by birth month (in the club dashboard)
This does not replace your own awareness – but it provides you with the data to make fair decisions.
Read more: Bayern, Dortmund und das deutsche NLZ-System.
Read more: Athletic Bilbao: Wie Lezama ausbildet.
Frequently Asked Questions about the Relative Age Effect
Conclusion: You cannot solve the RAE alone – but you can stop reinforcing it
The Relative Age Effect is a systemic problem in youth football. As an individual coach, you cannot eliminate it single-handedly. But you can stop reinforcing it unconsciously.
Conscious distribution of playing time, fair assessment in the context of birth months, actively recommending late developers, educating parents – these are practical levers you hold as a coach.
Over the years, this compounds. Players you have treated fairly will develop completely differently than if you had written them off after 6 months.
Try 30 days free of Coach OS for fair player development tracking →
Coach OS is the platform for football training session planning. Featuring player profiles that document birth months and development trajectories. Made in Hamburg.