What the research actually says
The relationship between IQ and life outcomes is one of the most studied topics in all of psychology. The findings are robust, replicable, and more nuanced than the simplified versions presented by either IQ enthusiasts or IQ sceptics.
The bottom line from decades of research: IQ is the single best-validated predictor of a wide range of important life outcomes. It also explains a minority of the variance in most outcomes — which means other factors (personality, motivation, social skills, circumstances) matter at least as much.
IQ and job performance
The most rigorous evidence comes from the industrial-organisational psychology literature. A 1998 meta-analysis by Schmidt and Hunter, synthesising results from 85 years of research on personnel selection, found that general mental ability (IQ) has a validity of approximately r=0.51 for predicting job performance — higher than any other single predictor including job experience, interviews, and personality tests.
The effect scales with job complexity. For complex professional roles (physician, engineer, lawyer), IQ validity approaches r=0.6–0.7. For simple, routine jobs with narrow task requirements, the relationship is weaker. The implication: IQ matters more in jobs that demand novel problem-solving, complex learning, and adaptive reasoning — less in jobs that rely on fixed procedures.
IQ and income
The correlation between IQ and income is typically around r=0.3–0.4, lower than the job performance relationship. Part of the difference reflects the role of non-cognitive factors in career advancement, negotiation, social networking, and risk-taking. IQ influences how well you do your job; income also depends on how well you navigate institutions, markets, and relationships.
The income-IQ relationship also varies by country and labour market. In societies with high returns to education and cognitive work, the relationship is stronger. In more egalitarian labour markets with compressed wages, it is weaker.
IQ and academic achievement
The relationship between IQ and academic grades is strong (r≈0.5–0.6) but far from perfect. Conscientiousness — one of the Big Five personality dimensions related to diligence, organisation, and self-discipline — adds significant incremental prediction of grades above and beyond IQ. A high-conscientiousness student with average IQ often outperforms a low-conscientiousness student with high IQ.
What IQ misses
IQ tests do not measure creativity, emotional intelligence, practical intelligence (what Sternberg calls "street smarts"), motivation, persistence, courage, or social competence. Research by Angela Duckworth on "grit" (passion and perseverance for long-term goals) finds that grit predicts achievement in high-demand contexts independently of IQ.
For entrepreneurial success specifically, risk tolerance, network quality, timing, and luck play enormous roles. Many of the most successful entrepreneurs in history had above-average but not exceptional IQs. The correlation between IQ and entrepreneurial success is weaker than between IQ and professional performance in structured settings.
The threshold hypothesis
A widely cited but contested idea in creativity research is the "threshold hypothesis": above an IQ of approximately 120, the relationship between IQ and creative achievement becomes negligible, and personality factors (openness to experience, tolerance for ambiguity) dominate. The evidence for a hard threshold is mixed — some studies find it, others find a continuous relationship — but the general principle that IQ effects on creative output attenuate at higher levels is reasonably well supported.
An honest summary
IQ matters. It is the most valid single predictor of the outcomes we typically call "success" in academic and professional domains. But it operates alongside personality, motivation, relationships, and circumstance — all of which matter substantially and are often more within your control.
The people who overstate IQ's importance (claiming it determines everything) and those who dismiss it as meaningless (usually for ideological reasons) are both distorting the evidence. The truth is more nuanced: IQ is a real, important variable that explains a meaningful but limited portion of human outcomes.