What Is the Average IQ?

The average IQ is 100 - here is what that actually means

Every modern IQ test is calibrated so that the average score in a representative sample of adults is 100, with a standard deviation of 15. This is a design choice, not a discovery. The raw test results - how many items each person got right - are scaled so that the average comes out at 100 and one standard deviation equals 15 points.

This convention dates to David Wechsler in 1939, who replaced the older "ratio IQ" (mental age divided by chronological age, multiplied by 100) with a "deviation IQ" centered on the population mean. The Wechsler scales (WAIS, WISC) and the Stanford-Binet have both used this calibration for decades, and online tests follow the same standard.

So "the average IQ is 100" is true by construction. The interesting question is what falls into the "average range" around it.

The "average range" of IQ scores

Conventionally, the average range covers one standard deviation either side of the mean - IQ 85 to 115. This range captures about 68% of the population.

About half of people score between 90 and 110 (the IQR), so most adults you meet have IQs in that narrower band. Scores outside the 70-130 range are unusual: about 1 in 44 people, in either direction.

The Flynn effect: average IQ has been rising

One of the most surprising findings in 20th-century psychology is that raw IQ scores rose steadily throughout the century. James Flynn documented this in 1984, showing that average test performance increased by roughly 3 IQ points per decade in developed countries. The phenomenon now bears his name.

The implication: a person scoring 100 on a 1950s test would score about 80 on a modern test, calibrated against the modern population. Tests have to be re-normed every 10 to 20 years to keep the mean at 100. The 1955 WAIS, 1981 WAIS-R, 1997 WAIS-III, and 2008 WAIS-IV each lowered scores relative to their predecessors because the underlying population had improved.

Causes are debated. The most cited factors:

• Better nutrition - especially in the first few years of life
• More years of schooling - modern populations average 12+ years vs 6 to 8 a century ago
• Reduced disease burden - infections in childhood reduce later IQ; modern medicine reduces them
• Greater test familiarity - modern people are more used to abstract, decontextualized problem-solving
• Smaller families - more cognitive resources per child

Recent data complicates the story: the Flynn effect has stalled or reversed since the 1990s in Norway, Denmark, the Netherlands, Finland, and the UK. Whether this is real cognitive decline, a change in what tests measure, or an artifact of test selection is hotly debated.

National IQ differences are complicated

When researchers administer the same test in different countries, measured averages do differ. A frequently-cited compilation by Lynn and Vanhanen (2002, 2012) reported national IQ estimates ranging from the mid-60s to the high 100s. These numbers have been used to argue for innate group differences.

The data are problematic for several reasons:

• Most low-IQ estimates come from samples of children, often non-representative, often using tests not normed locally
• The Flynn effect implies that countries earlier in their development trajectory will score lower - this is consistent with the data
• When matched on education, nutrition, and health, between-country differences shrink dramatically
• Within-country variation is always much larger than between-country variation

The mainstream interpretation is that measured national differences reflect developmental conditions - nutrition, schooling, public health, test familiarity - not innate cognitive differences between populations. The fact that East Asian average scores have caught up to Western scores in a single generation supports this view.

What about your IQ vs the average?

The most useful interpretation of your own IQ score is the percentile. If you score 120, you are at about the 91st percentile - meaning your score is higher than 91 out of every 100 people in the calibration population. This is more informative than the raw IQ number because it directly communicates rarity.

A few honest reminders:

• A single test score has measurement error of 5 to 15 points; do not over-interpret one result
• Most life outcomes depend more on conscientiousness, motivation, and luck than on IQ within the average range
• Differences within 5 points are not meaningful at the individual level - that is within measurement noise
• Above 130, the rarity grows fast, but so does the measurement uncertainty