5 min read · Updated 2026-06-01
Average IQ by age: what actually changes over time
IQ scores are age-normed, so the average is 100 at every age. What actually changes with age is fluid vs crystallised ability — here's the difference.
The short answer: the average IQ is 100 at every age. That's not a trick — it's how the scale is built. IQ scores are age-normed, so a 20-year-old's raw score is compared to other 20-year-olds, and a 60-year-old's is compared to other 60-year-olds.
What does change with age
Psychologists split reasoning ability into two broad kinds:
- Fluid ability — solving novel problems, spotting patterns, working under time pressure. Peaks in the mid-20s and gradually declines through adulthood.
- Crystallised ability — vocabulary, general knowledge, learned skills. Rises steadily and can keep improving into the 60s and 70s.
A standard IQ score blends both, which is why the age-adjusted average stays flat. If you looked at raw scores instead of age-normed ones, older adults would score lower on fluid tasks and higher on vocabulary — the two effects roughly cancel.
The Flynn effect
Across generations, raw IQ scores have been rising by roughly 3 points per decade in most developed countries — the Flynn effect. Test publishers periodically re-norm their tests to keep the average at 100. This is why an IQ of 100 in 1950 is not the same raw performance as an IQ of 100 today.
What this means for you
If you take an IQ test at 25 and again at 55, expect roughly the same score. If your score dropped a lot, that's worth investigating — but if it drifted by a few points, that's normal measurement noise.
Frequently asked questions
- What's the average IQ for a 20-year-old? A 40-year-old?
- 100 for both. IQ scores are age-normed, so the average is 100 at every age.
- Does IQ decline with age?
- Age-normed IQ scores don't decline. Raw performance on fluid tasks (novel problem-solving) does decline gradually after the mid-20s; raw performance on crystallised tasks (vocabulary, knowledge) keeps rising.
- What is the Flynn effect?
- The observation that raw IQ scores have risen by about 3 points per decade across generations. Test publishers re-norm periodically so the average stays at 100.