Average IQ by Age
Published by My Path · Founder: Peter Janicki, MSc Medical Psychology
People often assume IQ is a fixed number that rides along unchanged from childhood to old age. It isn't, and the reason is built into how a clinical score is constructed. Your rank among people your age is fairly stable, but the raw abilities underneath it rise, peak and shift across your life, and they do not all move at the same time. Keeping those two ideas apart answers most of the worry people have about aging and intelligence.
The key trick: clinical scores are age-normed
A clinical IQ score, from a test such as the WAIS-5 for adults or the WISC-V for children, is age-normed. The publisher tests a large sample in each age band, and your answers are compared only with the people in your band. An IQ of 100 for a ten-year-old means "average for a ten-year-old", not that the child reasons like an average adult. That is why the average is 100 at every age, and why a stable score across decades does not mean your abilities froze: it means you held your position among peers who were aging alongside you.
The lifespan trajectory
What actually changes is the balance between fluid ability (reasoning about new problems) and crystallized ability (accumulated knowledge), and different parts of each peak at different ages:
| Life stage | What tends to happen |
|---|---|
| Early childhood | Fast growth; single scores are noisy and predict adult ability only loosely |
| ~Age 10–12 | Rank becomes much more stable and predictive of adult ability |
| Late teens–20s | Processing speed peaks first; fluid reasoning and memory peak in the 20s |
| 30s–50s | Gradual decline in speed and fluid reasoning; vocabulary and knowledge grow |
| 60s and beyond | Further slowing on speeded and memory tasks; vocabulary holds up longest |
Childhood and adolescence: a moving foundation
In early childhood, test scores are genuinely noisy, and one early result predicts adult ability poorly. By late childhood, rank becomes far more stable. In the Scottish Mental Survey follow-up, scores at age 11 correlated about .63 with scores on the same test at age 77 (Deary et al., 2000). That is strong for a gap of 66 years, but it still leaves plenty of room for individual change, which is visible even within the teenage years (Ramsden et al., 2011).
Late teens and the 20s: speed first, then reasoning
Abilities do not peak together. In a study of tens of thousands of online participants, raw processing speed peaked earliest, around the late teens or early 20s, while other abilities peaked later (Hartshorne & Germine, 2015). Fluid reasoning and working memory are typically at or near their best in the 20s.
The 30s to 50s: depth replaces speed
Using large samples, Timothy Salthouse concluded that some decline in reasoning, speed and memory is already detectable in healthy, educated adults in their 20s and 30s (Salthouse, 2009). It is gradual. Meanwhile crystallized knowledge keeps growing: in the same study by Hartshorne and Germine, vocabulary peaked only in the late 60s or early 70s. A larger store of patterns, words and experience often makes people more effective at their work in midlife, because they recognize situations they have effectively seen before.
The senior years: slowing, not collapse
After 60, further slowing on speed-dependent and short-term memory tasks is normal. Vocabulary and general knowledge stay comparatively stable. Physical health, social engagement and continued mental activity are all associated with better cognitive aging, though in observational studies it is hard to separate cause from effect.
The big picture: speed for depth
The most useful way to hold all this is to stop thinking of intelligence as a single dial that only goes down. Across adulthood you tend to lose some raw speed and gain knowledge, context and judgment. For the long-run data behind this, including the cohorts followed from age 11 into their 90s, see why the average IQ is 100 at every age on our sister site, My IQ Path.
See where you stand today
Clinical IQ scores are age-normed. My Path's estimate is not: it compares you with everyone who sat the same form on this site, whatever their age, so read it as a position in that group, not an age-adjusted IQ. The test has a 12-item short form and a 60-item full form, both free, covering six areas: fluid, verbal, numerical and spatial reasoning, working memory and processing speed. The result shows your percentile among people who took the same form, its range, and that position re-expressed as an estimated IQ (≈ N, with a range). It is an estimate, not a clinical IQ.
If you're thinking about cognition across a career rather than a single moment, the career assessment and the Big Five help connect your evolving strengths to the kind of work that fits them.
Sources
- Deary, I. J., Whalley, L. J., Lemmon, H., Crawford, J. R., & Starr, J. M. (2000). The stability of individual differences in mental ability from childhood to old age: Follow-up of the 1932 Scottish Mental Survey. Intelligence, 28(1), 49–55. doi:10.1016/S0160-2896(99)00031-8
- Ramsden, S., Richardson, F. M., Josse, G., Thomas, M. S. C., Ellis, C., Shakeshaft, C., Seghier, M. L., & Price, C. J. (2011). Verbal and non-verbal intelligence changes in the teenage brain. Nature, 479(7371), 113–116. doi:10.1038/nature10514
- Hartshorne, J. K., & Germine, L. T. (2015). When does cognitive functioning peak? The asynchronous rise and fall of different cognitive abilities across the life span. Psychological Science, 26(4), 433–443. doi:10.1177/0956797614567339
- Salthouse, T. A. (2009). When does age-related cognitive decline begin? Neurobiology of Aging, 30(4), 507–514. doi:10.1016/j.neurobiolaging.2008.09.023