What Your Birth Month Says About You
Beyond horoscopes and folk wisdom, real scientific research has found measurable links between birth month and personality, health, and life outcomes. Here is what the data actually says — and why these patterns exist.
The Science Behind Birth Month Effects
Birth month research has generated hundreds of peer-reviewed studies. The findings are often surprising — not because the month itself has magical properties, but because the season of birth correlates with real biological and social factors:
Vitamin D & Sunlight
Maternal vitamin D levels during pregnancy vary dramatically by season. Deficiency has been linked to higher risk of certain conditions including multiple sclerosis, schizophrenia, and some autoimmune conditions.
The Relative Age Effect
Being the oldest or youngest child in a school cohort creates compounding advantages or disadvantages in education, sports selection, and early confidence-building that can persist for decades.
Seasonal Infections
Exposure to viruses and infections during critical developmental periods (both prenatal and early childhood) varies by season, influencing immune system calibration.
Maternal Nutrition
The availability of fresh produce and dietary patterns varies by season, affecting the nutritional environment during key prenatal development windows.
Your Birth Month — What Research Says
January
Disciplined, analytical, ambitiousHealth research
Studies link January births to slightly higher rates of schizophrenia (1–5%) — linked to prenatal vitamin D deficiency in winter pregnancies.
Research finding
January babies are statistically over-represented among general managers and CEOs in business research.
February
Creative, independent, idealisticHealth research
February births correlate with slightly elevated rates of sleep disorders in some studies.
Research finding
February has the fewest births of any month, meaning February-born people are among the rarest by birthday.
March
Optimistic, empathetic, adaptableHealth research
March babies show slightly lower rates of cardiovascular disease in some Northern Hemisphere studies.
Research finding
Research from the University of Vienna found March births are linked to occupations requiring long-term planning — architects, pilots, and surgeons.
April
Assertive, courageous, directHealth research
April births have been associated with slightly lower rates of asthma in children, possibly due to the springtime in utero vitamin D environment.
Research finding
A 2013 Columbia University study found April-born people score highest on a hyperthymia scale — a tendency toward consistently elevated, positive moods.
May
Persistent, sensual, dependableHealth research
May babies tend to have the highest birth weights on average, possibly due to optimal maternal nutrition in late pregnancy.
Research finding
People born in May self-report the highest life satisfaction scores in several large UK surveys. They also have the lowest incidence of seasonal affective disorder (SAD).
June
Versatile, sociable, romanticHealth research
June babies benefit from high maternal vitamin D levels — linked in some studies to better bone density outcomes.
Research finding
June is one of the most common birth months for athletes in sports with December 31 age cutoffs (like US youth soccer), due to the relative age effect.
July
Protective, tenacious, intuitiveHealth research
July births in the Northern Hemisphere correlate with slightly lower risk of multiple sclerosis — likely due to peak summer vitamin D exposure during key developmental months.
Research finding
July is consistently one of the most common birth months globally. The average person you meet is more likely to have been born in July than in any other month.
August
Confident, generous, perfectionistHealth research
The "relative age effect" hits August babies hardest in academic systems with September start dates — they are the youngest in their class year and often initially labelled as behind.
Research finding
A famous Malcolm Gladwell observation: the majority of elite Canadian hockey players are born in January–March, and the fewest are born in October–December — a direct consequence of the relative age effect in youth sports.
September
Methodical, meticulous, practicalHealth research
September births benefit from the relative age effect in countries with September school start dates — they are the oldest in their class and consistently outperform peers academically in early years.
Research finding
Studies in multiple countries show September babies are statistically more likely to attend university and earn more in early adulthood — entirely because of being oldest in their school cohort.
October
Balanced, charming, decisiveHealth research
October babies have been found in several studies to have lower-than-average risk of cardiovascular disease — a pattern researchers tentatively link to seasonal patterns in maternal diet.
Research finding
Research published in the Journal of Aging Research found October-born people have an above-average chance of living past 100, along with November and December births.
November
Intense, determined, magneticHealth research
November is Scorpio territory in Western astrology — more practically, November babies are the most common birth month in many US datasets, possibly due to Valentine's Day conceptions.
Research finding
A study in the International Journal of Sports Medicine found November-born soccer players are significantly over-represented among elite European leagues — partly because November falls just after the January 1 age cutoff used in most European youth football systems.
December
Adventurous, optimistic, generousHealth research
December babies face the double challenge of often being the youngest in their school year AND sharing their birthday season with major holidays — the social pressure of "holiday birthday" syndrome is a documented psychological phenomenon.
Research finding
Despite the relative age disadvantage in school, research from the UK finds December babies are among the most likely to become professional athletes — possibly because late bloomers who survive youth sports selection tend to be genuinely talented.
The Relative Age Effect: The Most Consequential Birth Month Factor
Of all birth month effects, the relative age effect (RAE) is the most extensively documented and the most practically significant. First described in the context of Canadian youth hockey by researcher Roger Barnsley in 1985, the RAE has since been found in education systems, professional sports, and business leadership studies across dozens of countries.
The mechanism is straightforward: when children are grouped by academic year with a fixed cutoff date, the oldest children in the cohort have had months more of cognitive and physical development than the youngest. At age 6, an eleven-month age gap represents roughly 15% of the child's entire life experience. Teachers identify the older children as “gifted,” select them for advanced tracks, and give them more positive feedback. The effect compounds.
Malcolm Gladwell popularised this finding in Outliers (2008), noting that the majority of elite Canadian NHL players were born in January, February, and March — the months immediately following the January 1 hockey age cutoff. The same pattern appears in European football, baseball, and cricket.
Crucially, the relative age effect is not about the calendar month per se — it is about proximity to the cutoff date. If school years started in July, July babies would have the same systematic advantages that September babies currently enjoy in the UK, or January babies in the US youth sports context.
Frequently Asked Questions
Does birth month actually affect personality?
The scientific evidence is mixed. Several large studies have found statistically significant correlations between birth month and certain personality traits, health outcomes, and career patterns. However, the effect sizes are generally small — birth month is a weak predictor at the individual level. The most well-established effects are the "relative age effect" (where being oldest or youngest in a school cohort affects educational and athletic outcomes) and vitamin D-related health effects (since vitamin D availability during pregnancy varies by season).
What is the relative age effect?
The relative age effect (RAE) is the phenomenon whereby children born just after the school year's cutoff date (and therefore the oldest in their cohort) significantly outperform those born just before it (the youngest). This advantage is particularly pronounced in early education and youth sports. A child who is 11 months older than a classmate at age 6 represents a 15% developmental difference — enormous at that stage. The effect can persist into adulthood through compounding advantages in confidence, selection, and coaching.
Why are some birth months more common than others?
Birth rates in many countries peak in late summer and early autumn (July–September in the US and UK), approximately nine months after the winter holiday season. Some researchers point to increased indoor activity and intimacy during cold winter months. There are also smaller spikes around nine months after Valentine's Day (November). The least common birth months in the US are typically January and February.
Is there a birth month linked to longer life?
A study published in the Journal of Aging Research analysed 1,574 centenarians (people who reached 100) in the US and found that those born in the autumn (September, October, November) were significantly over-represented compared to those born in the spring. The researchers theorised this relates to seasonal variation in maternal health, vitamin D availability, and early childhood disease exposure. However, these are population-level statistical patterns — individual longevity depends overwhelmingly on lifestyle, genetics, and healthcare access.
What birth month produces the most successful people?
Studies of CEOs, US presidents, and high-earning professionals tend to find over-representation of people born in certain months depending on the country's school start date. In the US (September school start), September and October births show advantages. In the UK (September school start), again September and autumn birthdays are advantaged. These effects are not destiny — they reflect systemic selection biases in early education and sport, not any inherent ability difference.
Explore More Birthday Science
Find out what day of the week you were born, count down to your next birthday, or calculate your exact age.