What Is the Average IQ? The Number 100 Explained

The average IQ is 100 — not by accident, but by design. IQ tests are built and re-scaled so that the typical score in the population always works out to 100, with most people clustered close to it. So the more useful questions are: what counts as the normal range, and why is the average fixed at 100 in the first place?

Why the average is always 100

An IQ score is relative, not an absolute count of correct answers. Test makers give a fixed set of problems to a large, representative sample, then scale the raw results so the mean lands on 100. Your IQ tells you where you sit relative to that average, not how many items you solved. We walk through that conversion in what an IQ test is and how IQ is measured.

Because the average is defined as 100, it stays at 100 even as tests are revised — publishers periodically re-norm their tests to keep it there. That re-norming matters: raw performance has actually drifted upward over the twentieth century, a pattern known as the Flynn effect (Flynn, 1987), and re-standardization is what keeps the average pinned at 100 despite it.

The normal range: 85 to 115

On the most common scale, the standard deviation is 15 points, and scores follow an approximately normal distribution — the bell curve. From that shape:

• About 68% of people score between 85 and 115 — the usual "average" or "normal" band.
• About 95% score between 70 and 130.
• About 2% score above 130, and about 2% below 70.

So when people ask whether their score is "good," the honest answer is that anything in the 85–115 band is squarely typical. For where the lines between bands fall, see the IQ scale explained and what a good IQ score means; for the distribution itself, the IQ bell curve.

Average IQ and age

A frequent point of confusion: does the average change as you get older? Because scores are age-normed, the average is held at 100 within every age group, so a 25-year-old and a 65-year-old at "average" both score around 100 against their own peers. Underlying abilities do shift with age — fluid reasoning tends to peak earlier, crystallized knowledge later — which we cover in average IQ by age.

Average IQ by country

You will also see tables ranking nations by average IQ. Treat them with real caution: they mix together very different tests, samples, languages and schooling conditions, and the best-known datasets have been widely criticized. We unpack why in average IQ by country. The short version is that environmental factors — health, nutrition and education — explain far more of the apparent differences than the rankings imply.

The takeaway

The average IQ is 100 because tests are designed that way, and most people fall in the 85–115 band around it. A single score is a snapshot against a peer group, not a verdict on a person. If you want to see roughly where you sit, an age-normed test like ours gives a quick estimate — just read it alongside the margin of error we describe in how accurate online IQ tests are.