Average IQ by Age: How Intelligence Changes Over a Lifetime

Why the average is always 100

IQ tests don't compare a 25-year-old to a 70-year-old directly. Each person's raw score is converted against a representative sample of people their own age. That normalization is what keeps the average pinned at 100 for every age group — so 'average IQ by age' is, on the IQ scale itself, always 100.

Two kinds of intelligence age differently

Psychologists distinguish two broad abilities. Fluid intelligence is your capacity to reason about new problems and process information quickly. Crystallized intelligence is your accumulated knowledge, vocabulary and expertise.

• In cross-sectional studies, measures of reasoning, processing speed and memory show a nearly linear decline from early adulthood, while vocabulary and general knowledge increase until at least the 60s.
• Studies that follow the same people over time sometimes show stability or even gains, partly because people improve on tests they have taken before.
• Growing knowledge doesn't simply cancel out the decline: people whose fluid abilities fall more tend to gain less in crystallized abilities, too.

Raw performance across the lifespan

There is no single curve for "raw intelligence". Different abilities rise and fall at different rates, cross-sectional and longitudinal studies paint somewhat different pictures, and people differ widely at every age. One large study found that some abilities peak around the end of high school, some plateau in early adulthood and decline from the 30s, and others don't peak until the 40s or later. Throughout, your normed IQ stays centered on 100 for your age group.

A note on children and teens

Children are assessed with their own tests and norms, individually, by a qualified professional. A single score is a narrow basis for decisions about a child, which is one reason professionals draw on more than one source of information — and why online tests are not appropriate for assessing kids.

Does your IQ change as you age?

This is where two questions get tangled. The first is whether your normed IQ score — your standing relative to others your age — moves over time. The second is whether your raw cognitive abilities change. The answers differ, and confusing them is the source of most myths about IQ and aging.

For adults, normed IQ scores are relatively stable. Someone who scores above average at 25 will usually still score above average decades later, because age-norming compares them to other people their age at each point. Studies that tested the same people at age 11 and again in old age found differences between individuals to be highly stable. Your rank doesn't swing wildly just because you had a birthday — though scores can still move with education, health, major life events, or simple measurement error.

The Flynn effect: change across generations

There's a third kind of change that has nothing to do with individual aging: the Flynn effect. Across much of the twentieth century, average raw scores on IQ tests rose from one generation to the next. A meta-analysis of 271 samples from 31 countries estimated gains of about 0.28 full-scale IQ points a year — roughly 3 points per decade — with smaller gains in recent decades.

What caused the rise is still debated. The authors of that meta-analysis attribute the overall trend mainly to "life history speed" factors, and the differences between ability domains to social multiplier effects and economic prosperity. In some countries the gains have stopped or reversed — in Germany, for example, a study of secondary-school students found declines in figural reasoning between 2012 and 2022.

Can your IQ actually rise or fall?

Within limits, measured IQ can move. Education has the clearest evidence: a meta-analysis found gains of about 1 to 5 IQ points per additional year of education, lasting across the lifespan. In the other direction, poor sleep, chronic stress, depression, brain injury and some illnesses can impair thinking.

What you generally cannot expect is a quick, large, permanent jump from brain-training apps or puzzle routines: a major review found extensive evidence that training improves the trained tasks, but little evidence that it improves distantly related tasks or everyday thinking. The National Institute on Aging points to several things linked to cognitive health as people age:

• Staying physically active.
• Managing chronic conditions such as high blood pressure, diabetes, high cholesterol and depression.
• Getting enough sleep — generally seven to eight hours a night.
• Managing stress.
• Learning new skills may help, although evidence of a lasting effect is limited.