Why the average is exactly 100
An IQ score is a rank, not a quantity. When a test is built, it is given to a large norm sample, usually around 2,000 people chosen to match the population by age, sex, region and education. Raw scores are then converted so that the sample's mean becomes 100 and one standard deviation becomes 15 points.
A score of 115 therefore means you did better than about 84% of the norm sample, and 130 means better than about 98%. On a properly normed test the average cannot drift away from 100, because 100 is defined as the average.
This has a practical consequence. When someone says the average IQ is "going down" or "going up", they mean that raw performance has changed relative to an older norm sample. Once a test is re-normed, the new middle is set back to 100. The number itself carries no information about how clever a population is in absolute terms; only the comparison with the norm group does.
What counts as a normal IQ for an adult
Test publishers describe scores in bands rather than as single numbers, because any one test carries a measurement error of a few points. The classification below follows the bands used on Wechsler adult tests; the newest editions use plainer labels such as "high average" and "very high", but the cut-offs are the same.
"Normal" is wider than most people expect. Half of all adults sit between 90 and 109, and anything from 85 to 115 is within one standard deviation of the middle. A 97 and a 104 are, for practical purposes, the same result. See the IQ scale for what each band means, or IQ 100 for the middle of the curve.
| Band | IQ range | Share of adults |
|---|---|---|
| Very superior | 130 and above | 2.3% |
| Superior | 120–129 | 6.8% |
| High average | 110–119 | 16.1% |
| Average | 90–109 | 49.5% |
| Low average | 80–89 | 16.1% |
| Borderline | 70–79 | 6.8% |
| Extremely low | Below 70 | 2.3% |
Average IQ by age
Raw reasoning ability peaks in the early twenties and declines slowly from middle age. Processing speed falls fastest; vocabulary and general knowledge hold up into old age. IQ scores hide this on purpose. Adult tests are normed per age band, so a 65-year-old is compared with other 65-year-olds and a 25-year-old with other 25-year-olds.
The average IQ is therefore 100 at every age. What changes is the raw score needed to reach it. This is also why a test that never asks your age cannot give you an age-adjusted score. Children are scored the same way, against children of the same age, on tests built for them, such as the WISC-V for ages 6 to 16.
Online tests that skip age norming usually compare everyone with the same pool of visitors, who tend to be younger than the general population. For older adults that means the score can come out a few points lower than a properly age-normed test would give.
Average IQ in the United States
On a test normed in the United States, the US average is 100 by construction. Figures of 97 or 98 that circulate online come from national comparisons that score one country against another country's norms, often with small or old samples. Those comparisons are contested, and they answer a different question from "what is the average IQ".
What is well established is that raw scores in the US, as in most countries with expanding schooling and better nutrition, rose by about three IQ points per decade through much of the 20th century. This rise is called the Flynn effect, and it is the reason tests are re-normed every 10 to 20 years. A test with norms from 1990, taken today, would overstate your IQ by several points. Some countries, including Norway and Denmark, have seen the rise stall or reverse since the 1990s.
What an average score does and does not tell you
- IQ predicts school results fairly well (correlations around 0.5) and job performance moderately (estimates range from about 0.3 to 0.5 depending on the study). It is one of the better single predictors psychology has, and still leaves most of the variation to effort, personality and circumstance.
- A score in the 90 to 109 band says you reason about as well as most people. It says nothing about creativity, judgement, social skill or expertise.
- One test is one sample. Two good tests taken a few weeks apart usually differ by a few points. A gap of 10 or more points suggests at least one of them is not measuring what it claims. Our page on online IQ test accuracy explains how to tell.
Sources
Wechsler, D. WAIS-IV Technical and Interpretive Manual. Pearson, 2008.
Flynn, J. R. "Massive IQ gains in 14 nations: what IQ tests really measure". Psychological Bulletin, 1987.
Bratsberg, B. and Rogeberg, O. "Flynn effect and its reversal are both environmentally caused". PNAS, 2018.
Sackett, P. R. et al. "Revisiting meta-analytic estimates of validity in personnel selection". Journal of Applied Psychology, 2022.
Frequently asked questions
What is the average IQ?
100. IQ tests are scored so that the population mean is 100 and the standard deviation is 15. About 68% of adults score between 85 and 115.
What is a normal IQ for an adult?
Anything from 85 to 115 is within the normal range, and 90 to 109 is the "average" band that covers half of all adults. A score of 97 and a score of 104 are not meaningfully different.
What is the average IQ in the United States?
On US-normed tests it is 100 by definition. Figures such as 98 come from comparing countries against each other's norms, which is a comparison of samples rather than a national measurement, and those figures are disputed.
What is a normal IQ range?
70 to 130 covers about 95% of people. Scores below 70 fall in the "extremely low" band used in clinical assessment; scores of 130 and above are the top 2.3%, a common threshold for gifted programmes.
What is the average IQ score by age?
100 at every age, because tests are normed separately for each age band. Raw reasoning ability peaks in the early twenties and declines gradually, but the scoring compensates, so a 70-year-old with an IQ of 110 is ahead of about 75% of 70-year-olds.
What is a normal IQ test score?
On a well-normed test, most people land between 85 and 115. If an online test gives you 140 after ten easy questions, the test is flattering you. Serious tests report a range or confidence interval rather than a single exact number.
What is the average IQ score?
For the general population it is 100. On this site, the self-selected group who completed the free test averages 114.5 against provisional norms, which shows how much people who seek out IQ tests differ from the population.