Reference
What is the average IQ?
The average IQ is 100. That is not a measurement result — it is a definition, and understanding why clears up most of the confusion about what an average score means.
Why the answer is 100
The average IQ is 100 because the scale is constructed that way. Test publishers take a representative sample, examine the distribution of raw scores, and define the middle of that distribution as 100.
The consequence is that the average cannot drift. If the population got better at the test tomorrow, the test would be renormed and the average would be 100 again. If it got worse, same answer. The number is fixed by construction, not observed.
So the question “what is the average IQ” has a definitional answer, and the question people usually mean — how does my score compare to most people's — is answered by the percentile rather than the average.
100 is not the average amount of reasoning ability. It is the label we attach to the middle of whoever was in the norm sample.
What the average hides
An average with no spread is nearly useless, and the spread is the more informative half of the description.
| Range | Share of people | Description |
|---|---|---|
| 90–109 | 50% | The average band — half of everyone |
| 85–115 | about 68% | Within one standard deviation |
| 80–119 | about 82% | The great majority of people |
| 70–130 | about 95% | Within two standard deviations |
| Below 70 or above 130 | about 4.4% | Both tails combined |
The row that surprises people is the first one. Half the population sits in a twenty-point band around the mean, which means the overwhelming majority of competent professionals in every field are in it, simply because that is where most people are.
The average that keeps rising underneath
Here is the part that makes the definitional answer interesting rather than merely pedantic.
Raw performance on IQ tests rose throughout the twentieth century, at roughly three points per decade, in every country with long-running data. The rise does not appear in published scores because publishers renorm, resetting the average to 100 each time.
Score a modern sample against 1930s norms and the average lands somewhere around 120. That is the Flynn effect, and it is the strongest available evidence that a large part of what IQ tests measure is environmental rather than fixed.
Since the 1990s, several countries with good data — Norway, Denmark, Finland, the UK — have shown the rise flattening and reversing. The declines are small and not universal. The full story.
Does the average change with age?
No, because norms are age-banded. A 70-year-old is compared against other 70-year-olds, so the average for every age group is 100 by construction.
What does change with age is raw performance. Speeded and fluid-reasoning tasks decline from roughly the late twenties onwards; vocabulary and accumulated knowledge hold up or improve into the sixties and beyond. The age norms compensate for the first, which is why a 65-year-old and a 25-year-old with the same IQ score are not performing identically on the raw tasks.
National averages
Datasets of national average IQ circulate widely and should be handled with considerable care. They are compiled from studies that differ enormously in sample size, age range, representativeness and the instrument used, and several national figures are extrapolated from neighbouring countries rather than measured.
There is also a definitional problem that is rarely stated. If IQ is standardised so that the average is 100, a national average of 85 means something only relative to a specified reference population — usually a Western standardisation sample. It is a comparison against that sample, not a property of a country.
We publish the dataset with its caveats on average IQ by country, because people search for it and the version they find elsewhere usually arrives without any caveats at all.
What an average score means for you
If you scored in the average band, you are in the largest group there is, and the band contains most of the people doing most of the jobs. “Average” in psychometrics means typical, not deficient, and it covers a wider range of everyday capability than the word suggests.
If you scored above it, you have an advantage at tasks that reward fast pattern-learning, and the research is clear that plenty of people with higher scores do less with them. What the score predicts.
And whichever it was, the error band on a single test is wide enough that a good chunk of the difference between your result and someone else's is noise.
Questions
Questions people ask
What is the average IQ score?
100, by definition. The scale is built so that the middle of the norm sample scores 100, which means the average cannot drift away from it.
What is the average IQ by age?
100 for every age group, because norms are age-banded. Raw performance on fluid tasks declines with age while vocabulary holds up, and the age norms compensate.
Has the average IQ increased over time?
Raw performance rose by roughly three points a decade through the twentieth century — the Flynn effect — but the published average stays at 100 because tests are renormed. In several countries the rise has stopped or reversed since the 1990s.
What percentage of people have an average IQ?
About half of everyone falls in the 90–109 band. About 68 percent fall between 85 and 115.
Is an IQ of 100 good?
It is exactly typical — better than half of people and worse than the other half. In psychometrics 'average' means typical, and the band covers a wide range of everyday capability.
Find out where you land
Ten reasoning questions, an instant band and an explanation for every answer.