Average IQ: What Is the Average IQ Score?

The average IQ score is 100 on most modern IQ scales. The interesting part is why: 100 is the center because the test is built and normed to make it the center.

If you ask, “What is the average IQ?” the short answer is 100. But 100 is not a quantity of intelligence discovered in nature. It is the midpoint of a standardized scoring system. Test publishers collect performance from a carefully selected reference sample, build age-based norms, and convert raw test results onto a scale centered around 100.

That detail clears up most of the confusion around “average IQ.” It explains why the average can stay at 100 even when raw performance changes across generations, and why a 25-year-old and a 70-year-old can both score 100. For the broader foundation, What Is IQ? explains what the score itself represents.

Why Is the Average IQ 100?

Because modern IQ scores are standardized. A raw score — how many items you answered correctly, how quickly you completed certain tasks, or how you performed across subtests — has little meaning by itself. The important question is how that performance compares with the people used to create the test norms.

On widely used scales such as the Stanford–Binet, the mean is 100 and the standard deviation is 15. The APA Dictionary of Psychology gives those values directly for the current Stanford–Binet structure. Pearson’s current WAIS-5 materials likewise describe updated norms and interpretation relative to same-age peers.

So 100 is a landmark: the center of the normed distribution. It means performance around the middle of the relevant comparison group. It is not 100 questions correct, 100 percent of anything, or an absolute quantity of intelligence.

What Does “Average” Cover?

People often hear “the average IQ is 100” and imagine a razor-thin dividing line: 99 below average, 101 above average. Real scores are not useful at that level of precision. Measurement has uncertainty, and most people sit in a broad band around the center. On a scale with a 15-point standard deviation, roughly two-thirds of scores fall between 85 and 115 if the distribution follows the familiar bell-shaped pattern.

The exact percentile attached to 105, 115, 120, 130, or any other score belongs to a different question. Our IQ score chart lays out the ranges, percentiles, and bell curve.

Why Is the Average IQ Still 100 If Test Performance Changes?

This is where the scale gets interesting. Raw performance on intelligence tests can shift over decades. James Flynn’s classic 1987 analysis of 14 nations documented substantial generational gains on IQ-test performance, a pattern that became known as the Flynn effect. A later review by Richard Nisbett and colleagues likewise discussed continued gains across many populations and the importance of environmental influences on measured intelligence.

Yet a newly normed test can still average 100. When publishers update an assessment, they update the normative reference too. Pearson explicitly lists updated norms as a feature of the WAIS-5. If raw performance has moved, the conversion to standardized IQ moves with it.

Think of 100 as the center marker on a moving map. The landscape can change while the marker continues to indicate the middle of the current reference group. That is why comparing an IQ score from one test edition with a score from a much older edition requires more care than simply comparing the two numbers.

What Is the Average IQ by Age?

Once you think of 100 as a marker on a reference map, age norms become much easier to understand. Each age group gets its own reference map, and the center still sits at about 100. A 25-year-old who scores 100 is near the middle of the relevant 25-year-old norm group; a 70-year-old who scores 100 is near the middle of the relevant older group.

The underlying cognitive landscape can still change with age. Processing speed, accumulated knowledge, working memory, and other abilities do not all follow the same trajectory through adulthood. Age norming keeps the comparison fair by asking where someone stands among similar-age peers. Our companion guide Does IQ Change With Age? deals with the separate question of how those abilities themselves change.

That is how two people decades apart can arrive at the same standardized score through somewhat different raw performances. The number 100 stays put because the reference frame moved with them.

Is 100 the Average IQ Everywhere in the World?

The same reference-map idea becomes even more important when geography enters the picture. A test centered at 100 tells you about the population used to build its norms. It does not automatically make 100 the measured average of every country or population where someone might later use that test.

This is why country-by-country IQ tables deserve more caution than their tidy numbers sometimes invite. A decimal point can look impressively exact while the underlying comparison still depends on sampling, language, educational exposure, the test itself, and how well its norms fit the people being measured. Pearson notes, for example, that WAIS-5 was normed on primary English speakers and that language and culture matter when interpreting scores outside that context.

Change the reference population and you may be changing the map. The broader APA task-force report on intelligence is useful here because it emphasizes the context needed to interpret intelligence-test scores.

Does Scoring 100 Mean You Are “Exactly Average”?

By the time several kinds of cognitive performance have been compressed into one score, a lot of texture has disappeared. A result near 100 places the overall standardized score near the center of the comparison distribution. It says far less about the shape underneath. One person might pair strong verbal reasoning with slower processing speed; another could reach a similar total through a very different profile.

Even the position itself has a little blur around it. Scores contain measurement error, so professional reports may include confidence intervals rather than treating the observed number as perfectly exact. The attraction of IQ is that one number feels wonderfully definite. Good interpretation lets the edges stay slightly fuzzy.

Want to See What an IQ-Style 100 Feels Like?

Cognitive Train’s free IQ-Style Test lets you try verbal, logic, and visual-spatial question types and see a six-skill breakdown. Its scale is centered on 100 for the test’s own scoring system, so it gives you the familiar experience of an IQ-style number while stating clearly what that number represents. It is a performance score on this online test, not a professionally normed clinical IQ result.

The One Thing to Remember

The average IQ is 100 because IQ is a standardized, norm-referenced score. One hundred is an address in a reference system: roughly the center of this comparison group on this assessment. It is not a bucket containing 100 units of intelligence. Read the number as a location rather than a ruler mark, and the whole scale clicks into place.

Explore the wider science in the Brain Articles collection, browse individual brain tests and cognitive assessments, or use Cognitive Train’s free cognitive training and brain training tools to see different mental skills on their own.