IQ predicts success better than almost any other single measure psychologists have, and still leaves most of the outcome unexplained. Meta-analyses put the correlation with job performance at about 0.5, with years of education at about 0.5–0.6, and with income at about 0.2–0.3. A 15-point advantage shifts the odds meaningfully; it guarantees nothing. Conscientiousness, health, opportunity and luck fill the rest of the picture.
What the numbers say
| Outcome | Correlation with IQ (approx.) | Source |
|---|---|---|
| Job performance (all jobs) | 0.5 (higher in complex jobs) | Schmidt & Hunter meta-analyses, 1998 and later |
| Training success | 0.5–0.6 | Same |
| Years of education | 0.5–0.6 | Strenze 2007 meta-analysis |
| Occupational status | 0.4–0.5 | Strenze 2007 |
| Income | 0.2–0.3 | Strenze 2007; Zagorsky 2007 |
| Longevity | small but consistent | Scottish Mental Surveys follow-ups (Deary) |
A correlation of 0.5 means IQ accounts for about a quarter of the variation in the outcome. That is a lot by the standards of psychology, and well short of destiny. Two people with the same IQ routinely end up in very different places.
Why IQ matters most for complex work
The job-performance correlation is not uniform. In Schmidt and Hunter's data, general mental ability predicts performance at about 0.58 for professional and managerial jobs, 0.5 for skilled technical work and around 0.2–0.3 for routine manual work. The reason is learning: complex jobs require continually acquiring new knowledge and solving unfamiliar problems, which is what IQ tests sample. Once a job is learned, experience and conscientiousness take over much of the predictive load.
This is why many employers use cognitive tests in hiring for roles with a long learning curve, and why they add structured interviews and work samples — adding a good second predictor raises validity more than squeezing another point out of the first.
Income: a real but modest link
Jay Zagorsky's 2007 study of about 7,400 Americans found that each IQ point was associated with roughly $200–$600 more annual income, but with no relationship to wealth once income was accounted for: higher-IQ people were no better at keeping money, and were as likely to have maxed out credit cards. Tamás Strenze's meta-analysis found that the IQ–income correlation (around 0.2) was weaker than the IQ–education link, and that parental socioeconomic status predicted income almost as well as IQ did. Intelligence opens doors; it does not walk through them for you.
What matters besides IQ
- Conscientiousness — the Big Five trait of diligence and self-control predicts job performance at about 0.2–0.3 across jobs and adds to IQ rather than overlapping it. Our Big Five test measures it.
- Health and stability — chronic illness, poor sleep and financial stress reduce the performance that any level of ability can deliver.
- Opportunity — family background, schooling and location still shape outcomes strongly, independent of ability.
- Chance — being in the right place with the right skill at the right time; the part no test measures.
“Emotional intelligence” is often listed here as well. The evidence is that EQ measures overlap substantially with personality and, once IQ and conscientiousness are accounted for, add only a little to the prediction of job performance. See IQ vs EQ for the comparison.
How to read your own score
A score of 115–125 is the range in which most professionals, engineers and managers fall; above 130 is typical for research scientists and top-ranked university graduates, but plenty of people in those jobs score lower and do fine. A score below average does not close any particular door, and most careers are learnable with persistence. If you want to know where you stand, the free IQ test takes about eight minutes; the reading guide is in what your IQ score actually means.
Frequently asked questions
Does a high IQ guarantee success?
No. Correlations of 0.2–0.5 leave most of the variation in success unexplained. Many high-IQ people have ordinary careers, and the famous Terman study of gifted children found that persistence and confidence separated the most successful from the least.
What IQ do you need to be a doctor or lawyer?
There is no cut-off. Studies of professional groups find averages around 120–125 with wide ranges; people in the 100–110 band qualify and practise successfully every year.
Is IQ or hard work more important?
Both contribute, and they are roughly independent. In most studies conscientiousness predicts outcomes about half as strongly as IQ, and the two add up rather than substitute.
Does IQ predict happiness?
Barely. Correlations between IQ and life satisfaction are close to zero once income and health are accounted for.
Know your number
The free IQ test gives you a score and a percentile in about eight minutes; the Big Five test covers the rest of the picture.
Take the Free IQ Test