Does IQ change with age?
Your position relative to your age group is fairly stable. The abilities underneath it are not: some peak in your twenties, others keep climbing into your sixties.
The trick in the question
IQ is age normed. You are compared to people your own age, not to the whole population.
Which means if everyone your age declines together on some ability, your score does not move. The question splits in two, with two different answers.
The score: fairly stable
Your position relative to your peers is durable.
The Lothian Birth Cohort studies are the best evidence available. Scottish children sat a national intelligence test at age eleven in 1932 and 1947, and researchers tracked down and retested the same people decades later. The correlations across roughly sixty years were substantial.
Substantial is not perfect. Individual trajectories vary, health events matter, and the correlation leaves real room for change in real people. But the broad picture is stability rather than drift.
The abilities: moving in opposite directions
Underneath the stable score, two broad kinds of ability behave quite differently. The distinction is fluid versus crystallized intelligence, and it does most of the explanatory work here.
Fluid abilities peak in early adulthood and decline gradually. Reasoning about novel problems, processing speed, working memory. This is why an unfamiliar puzzle feels harder at sixty than at twenty.
Crystallized abilities typically hold steady or keep improving well into later life. Vocabulary, accumulated knowledge, professional judgement.
The composite score conceals the trade because it averages the two, and age norming conceals it further. An older expert routinely outperforms a faster-reasoning novice in their own domain: raw speed lost, accumulated structure gained.
Childhood scores
Scores taken very early are unreliable predictors. Young children’s performance is noisy and developmental timing varies enormously. Stability improves markedly from around age ten.
Worth remembering when reading prodigy figures. A remarkable result at seven is a real observation about a seven-year-old and a much weaker statement about the adult, which is one reason the historical record claims are so difficult to interpret.
What actually degrades a score
More prosaic than ageing, and more actionable:
- Poor sleep
- Illness, particularly anything cardiovascular
- Untreated hearing or vision loss, which quietly depresses measured performance
- Depression and chronic stress
- Some medications
Several are treatable, and a decline that looks cognitive is sometimes none of those things. If a real change worries you, that is a conversation for a doctor rather than an online test. We list the things that genuinely help in how to increase your IQ.
On retesting yourself
If you take our free IQ test now and again in ten years, do not read the difference as a measure of ageing.
Short screeners are imprecise, practice effects push retest scores up, and sleep and stress move results by several points on any given day. The change you observe will mostly be noise.
Key takeaways
- IQ is age normed, so your score compares you to your own age group and stays relatively stable.
- Fluid abilities peak in early adulthood and decline gradually; crystallized abilities hold or improve.
- The Lothian Birth Cohort found substantial stability across roughly sixty years.
- Childhood scores become reasonably predictive from around age ten, not before.
- Sleep, cardiovascular health, untreated sensory loss and depression all move measured performance.
- Differences between two online test attempts are mostly noise, not real change.