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.

• Fluid intelligence tends to peak in the late teens through late twenties, then declines gradually.
• Crystallized intelligence keeps climbing through midlife and can stay strong into older age.
• This is why experience often compensates for slower raw processing as we get older.

Raw performance across the lifespan

The chart below illustrates relative performance on fluid-reasoning tasks by age group. Remember: this is raw performance, not your normed IQ score (which stays centered on 100 for your age).

A note on children and teens

Childhood IQ scores are less stable than adult scores — a young child's measured IQ can shift meaningfully as they develop. That's one reason professionals are cautious about labeling children based on a single test, 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, on average, tend to score above average at 55, because age-norming compares them to other people their age at each point. 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 substantially from one generation to the next — roughly a few points per decade in many countries.

Human genetics did not change over those few generations, so the rise is attributed to environmental factors: better nutrition, more and longer schooling, smaller families, greater familiarity with abstract problem-solving, and more cognitively demanding work. In some countries the gains have recently slowed or reversed.

Can your IQ actually rise or fall?

Within limits, measured IQ can move. Sustained education tends to nudge scores upward, and conditions that harm the brain — serious illness, injury, chronic sleep deprivation, heavy stress — can push raw performance down. These effects are real but usually modest, not the dramatic swings popular myths suggest.

What you generally cannot expect is a quick, large, permanent jump from brain-training apps or puzzle routines, which tend to improve the trained task without broadly raising general intelligence. The most reliable supports for cognitive performance across the lifespan are unglamorous:

• Staying physically active and managing cardiovascular and metabolic health.
• Continued learning and mentally engaging work or hobbies.
• Adequate sleep and management of stress and mood.
• Treating sensory loss (like hearing) and chronic conditions that strain cognition.