IQ Test Average: What Is an Average IQ Score?

Why the average is always 100

An IQ test does not measure something with a fixed unit, the way a scale measures weight. It counts how many questions you get right and then compares that count with the results of a large reference group, called the norm sample, tested when the test was made.

The comparison is turned into a standard score. Pearson, which publishes the Wechsler tests, describes a common version as a scale where "the mean is 100 and the standard deviation is 15." Whatever the raw scores of the norm sample were, their average becomes 100. So an average IQ of 100 says nothing about how clever people are in general. It says you scored at the middle of that test's reference group.

What the standard deviation means

The standard deviation measures how spread out scores are. On the IQ scale it is 15 points. A score of 115 is one standard deviation above the average, 130 is two, and 85 is one below.

IQ scales are built to follow the normal curve (the bell curve). Worked out from that curve:

• about 68.3% of people score between 85 and 115 (within one standard deviation),
• about 95.4% score between 70 and 130 (within two),
• about 99.7% score between 55 and 145 (within three).

Pearson's primer gives the same picture in percentiles: one and two standard deviations above the mean are the 84th and 98th percentiles, and one and two below are the 16th and 2nd. Real test results only follow the curve approximately, and least well at the extremes, where few people in any norm sample score.

Which scores count as average

There is no single official answer. Pearson's WISC-V report materials say that "scores ranging from 90 to 109 are typically considered average." Other writers use 85 to 115, the band within one standard deviation. On the normal curve the 90 to 109 band holds about half of all people (49.5%), and the 85 to 115 band about two thirds.

The IQ scale page has the full set of score ranges, how many people fall in each, and what the labels mean.

The average moves over time: the Flynn effect

Because 100 is fixed to a norm sample, the real level behind it can drift. In 1984 J. R. Flynn showed that every Stanford-Binet and Wechsler norm sample from 1932 to 1978 set a higher standard than the one before it. Over those 46 years the gain added up to 13.8 IQ points. This rise in test performance is now called the Flynn effect.

Later studies measured it more carefully:

• A 2014 meta-analysis in Psychological Bulletin (285 studies since 1951) found an average gain of 2.31 points per decade, and 2.93 points per decade for modern Stanford-Binet and Wechsler tests.
• A 2015 meta-analysis of 271 samples with almost 4 million people in 31 countries (1909 to 2013) found that the gains have become smaller in recent decades.
• A 2018 study of Norwegian military conscription scores (birth years 1962 to 1991) found that scores rose, reached a turning point and then declined. The same pattern shows up when siblings are compared, which the authors read as evidence that both the rise and the decline have environmental causes.

Why tests are re-normed

If performance drifts, an old norm table gives wrong scores. Pearson's primer says cognitive test norms "tend to shift approximately 3 to 4 points every 10 years" and that publishers update norms for this reason. The adult Wechsler test shows the cycle: the WAIS-IV was normed in 2007 and 2008, and its successor, the WAIS-5, in 2023 and 2024. At 3 to 4 points a decade, a score worked out from norms collected 20 years earlier can be several points off, only because the reference group was tested at a different time. The WAIS page explains how that test works.

How the average works on our test

Our test has 24 puzzles and a 20-minute limit. It has its own reference group: the people who take it. Until 500 valid first attempts are logged, we cannot measure where the middle is, so the score is a provisional estimate that assumes the average test-taker gets 12 of 24 right, with 4 puzzles as one standard deviation. Under that assumption 12 right gives 100, 16 right gives 115 and 8 right gives 85.

Once there are enough results, 100 means the middle of real people who took this version, and your score comes from where your raw score falls among them. Those people chose to take an online IQ test, so they are not a random sample of the population. The How the score works page explains both methods and their limits.