Average IQ by Age

If you Google "average IQ by age," you’ll find dozens of charts claiming a precise number for every age group: 90 at age 16, 105 at 35, 88 at 70. Almost all of them are wrong, or at least misleading.

The actual answer is more interesting, and once you understand it, every other question about age and intelligence becomes easier to think about clearly.

This guide walks through how IQ scores are calibrated for age, which cognitive abilities rise and which fall over a lifetime, and what you can reasonably conclude from your number at any point in life.

The short answer (and why it surprises people)

The average IQ in every age group is 100.

Not roughly 100. Exactly 100, by construction. That includes 12-year-olds, 30-year-olds, and 75-year-olds. Whatever age you are when you take a properly normed IQ test, the mean score for your age group is calibrated to land on 100, with a standard deviation of 15.

This is the part most online "average IQ by age" charts get wrong. They list different averages for different ages, as if the number drifts up through your 20s and decays after 60. It doesn’t, because that isn’t what the score is measuring.

How IQ tests are age-normed

When IQ tests are standardized, the test-makers gather a large normative sample, often several thousand people, stratified by age. They administer the same test to every group, then compute the score distribution within each age band separately.

Each age group’s raw score distribution is then mapped onto the standard IQ scale: mean 100, standard deviation 15. So a 25-year-old who answers, say, 47 of 60 matrix-reasoning items correctly might receive an IQ of 115, because that raw score is one standard deviation above the mean for 25-year-olds. A 65-year-old who answers 39 of 60 correctly might also receive an IQ of 115, because that lower raw score is one standard deviation above the mean for 65-year-olds.

Both people are at the same percentile within their cohort. Both receive the same IQ. But they are not solving the same number of problems.

This is the core mechanic and it has two consequences worth understanding before going further:

• Your IQ score doesn’t tell you how your cognitive performance compares to people of other ages. It tells you where you sit within your own age group.
• An IQ that stays steady across decades doesn’t mean nothing has changed. It means your performance has changed roughly in step with your peers.

The two curves: fluid vs. crystallized intelligence

To understand what age does to cognitive performance, you have to split intelligence into two components, a distinction first formalized by Raymond Cattell in 1963 and refined by John Horn through the 1980s.

Fluid intelligence

The ability to reason with novel problems where prior knowledge doesn’t help. Pattern recognition, mental rotation, working memory, and on-the-fly logical inference all sit here. Fluid intelligence depends heavily on processing speed and the integrity of the prefrontal cortex.

It rises sharply through childhood, peaks somewhere between the late teens and the mid-20s, and then declines gradually, roughly 1 to 2 IQ-equivalent points per decade in raw performance, accelerating slightly after 60 (Salthouse, 2009).

Crystallized intelligence

Accumulated knowledge: vocabulary, general information, verbal reasoning, domain expertise, learned procedures. Crystallized ability is the cognitive interest that compounds on top of fluid reasoning.

It rises through life and typically peaks somewhere between the ages of 50 and 70, then plateaus or declines very slowly. A 65-year-old retired professor likely outperforms a 25-year-old graduate student on vocabulary, analogies that depend on world knowledge, and well-rehearsed verbal reasoning, even though the same 25-year-old will outperform them on novel matrix problems.

Average IQ scores by age group

The table below shows what is actually happening underneath the score. The IQ column is constant by design; the changes are in the underlying cognitive performance, expressed as how a person of that age would score against the young-adult reference group.

The take-away: when someone says "average IQ at 70 is lower than average IQ at 25," they are usually conflating raw performance with the score itself. The score, by definition, doesn’t move. The performance does.

Childhood and adolescence: rapid growth, stabilizing scores

In children, raw cognitive performance grows so fast that test results from age 4 are only weakly predictive of results at age 14. The classic Scottish Mental Survey, which retested the same individuals at ages 11 and 77, found a correlation of approximately r = 0.66 between scores 66 years apart (Deary et al., 2004) — remarkably high, but considerably lower for children retested at ages 4 and 11.

To put that 66-year correlation in tangible terms: if you ranked 100 Scottish 11-year-olds by their IQ in 1932 and re-ranked the same 100 people by their IQ in 1998, the lists would not be identical — but they’d be much closer than chance. Roughly two-thirds of the rank ordering set in primary school survived nearly seven decades, two world wars, and the entire arc of an adult life. Few psychometric findings are as humbling.

Two implications:

• IQ scores in early childhood are noisy. They reflect the moment more than the trajectory.
• By the late teens, IQ becomes one of the most stable psychometric traits. Test-retest correlations across 50+ years routinely land in the 0.7 to 0.9 range.

Practically, the average IQ for teenagers is 100, just like every other age group. Teenagers often perform well on fluid-reasoning items because their fluid capacity is approaching its lifetime peak. They typically perform less well on items that lean on accumulated knowledge.

Adulthood: peak performance years

From the late teens to roughly age 30, fluid intelligence is at or near its lifetime peak. This is the window where novel-problem performance, mental rotation tasks, and unfamiliar pattern-recognition items tend to be most accurate to the underlying capacity.

From the 30s to the 50s, the picture diverges. Fluid reasoning has begun a gradual decline, while crystallized knowledge is still climbing. The composite IQ score reflects both forces at once, which is why average performance on full-battery IQ tests is so flat across these decades. People in their 40s often perform better on the verbal and information subtests than they did in their 20s, and slightly worse on the timed pattern-recognition subtests, with the two changes roughly canceling out.

This is also the period where individual differences in lifestyle start to matter most. Sleep quality, cardiovascular health, formal education, and work that demands sustained cognitive engagement all show measurable effects on age-related cognitive trajectory in longitudinal studies (Salthouse, 2006).

Older adulthood: what declines, what doesn’t

After 60, the curves start to separate more visibly.

What declines

• Processing speed. The clearest age-related shift. Reaction time and speed-of-perception measures drop steadily from the mid-20s onward and accelerate after 60.
• Working memory capacity. The number of items held in mind across multi-step problems declines modestly through middle age and more clearly after 70.
• Novel pattern recognition. Performance on first-time exposure to a new puzzle format slows and becomes more error-prone.

What stays high

• Vocabulary and verbal knowledge. Often higher at 70 than at 30.
• Domain expertise. Practiced reasoning within a familiar field stays largely intact, sometimes well into the 80s.
• Verbal fluency for well-rehearsed material. Speeches, professional writing, and routine analytical tasks within a familiar domain remain strong.

The composite IQ score in older adulthood is therefore a weighted average of these opposing forces. For most healthy older adults, the score lands close to where it was decades earlier, because the test is age-normed and because crystallized gains offset some of the fluid losses in raw terms.

What the score will not tell you is how much processing speed you’ve lost, or how much vocabulary you’ve gained. For that, you need a domain breakdown rather than a single number.

How to maintain cognitive performance with age

The literature is clearer here than most popular writing admits. The interventions with the strongest evidence for age-related cognitive maintenance are unglamorous and overlap heavily with general physical health.

1. Cardiovascular exercise. Regular aerobic activity has the most consistent evidence base for preserving fluid cognitive performance with age (Erickson et al., 2011). Walking 30 to 45 minutes most days clears the bar.
2. Sleep. Chronic short sleep is associated with measurable declines in working memory and processing speed independently of age (Lim and Dinges, 2010).
3. Cognitively demanding work or hobbies. Engagement with novel, effortful problems, especially those that resist routinization, is the closest thing the literature has to a cognitive maintenance lever. Rote crossword puzzles do less than learning a new instrument or a new domain.
4. Social engagement. Loneliness and social isolation predict accelerated cognitive decline in older adults, even after controlling for depression and physical health.
5. Treating hearing loss. Untreated hearing loss in midlife and older adulthood is one of the largest modifiable risk factors for later cognitive decline (Livingston et al., 2020).

What doesn’t hold up well in randomized trials: most commercial brain-training games, most "smart drug" supplements, and most claims that crossword puzzles preserve general cognition. They tend to make you better at the specific game or domain, not at fluid reasoning broadly.

Frequently asked questions

Related reading

• What Your IQ Score Actually Means — the 100-point scale, what it predicts, and what it doesn’t.
• Pattern Recognition Test — how matrix reasoning measures fluid intelligence, the kind that peaks early and declines first.
• Spatial Reasoning Test — another fluid-intelligence-heavy domain, with a notable peak in the 20s.
• Logical Reasoning Test — deductive reasoning, which responds to training across the lifespan.
• Numerical Reasoning Test — quantitative pattern detection, mostly fluid and stable from late teens.
• Verbal Reasoning Test — the crystallized-intelligence domain that keeps growing into your 60s.

References

1. Cattell, R. B. (1963). Theory of fluid and crystallized intelligence: A critical experiment. Journal of Educational Psychology, 54(1), 1–22.
2. Horn, J. L., & Cattell, R. B. (1967). Age differences in fluid and crystallized intelligence. Acta Psychologica, 26, 107–129.
3. Deary, I. J., Whiteman, M. C., Starr, J. M., Whalley, L. J., & Fox, H. C. (2004). The impact of childhood intelligence on later life: Following up the Scottish Mental Surveys of 1932 and 1947. Journal of Personality and Social Psychology, 86(1), 130–147.
4. Salthouse, T. A. (2006). Mental exercise and mental aging: Evaluating the validity of the "use it or lose it" hypothesis. Perspectives on Psychological Science, 1(1), 68–87.
5. Salthouse, T. A. (2009). When does age-related cognitive decline begin? Neurobiology of Aging, 30(4), 507–514.
6. Erickson, K. I., et al. (2011). Exercise training increases size of hippocampus and improves memory. Proceedings of the National Academy of Sciences, 108(7), 3017–3022.
7. Lim, J., & Dinges, D. F. (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychological Bulletin, 136(3), 375–389.
8. Livingston, G., et al. (2020). Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. The Lancet, 396(10248), 413–446.