The average IQ at every age is 100. IQ tests are age-normed: a 7-year-old is compared with other 7-year-olds and a 70-year-old with other 70-year-olds, so the typical person of any age scores 100. What changes with age is raw ability — how many questions you can answer — which rises through childhood, peaks at different ages for different skills, and declines in some areas later in life.
Average IQ by age: the short table
| Age group | Average IQ | Norms used (examples) |
|---|---|---|
| Ages 2–5 | 100 | WPPSI-IV norms; scores less stable, best seen as provisional |
| Ages 6–16 | 100 | WISC-V norms, by age band of a few months |
| Ages 16–19 | 100 | WAIS-IV / WAIS-5 norms begin at 16 |
| Ages 20–44 | 100 | Adult norms by age band |
| Ages 45–69 | 100 | Adult norms by age band |
| Ages 70–90 | 100 | WAIS-IV norms extend to 90 years 11 months |
So when people ask “what is the average IQ for a 13-year-old?” or “for a 40-year-old?”, the answer is always 100, with the same standard deviation of 15 and the same classification bands. A 10-year-old with an IQ of 120 and a 60-year-old with an IQ of 120 are both at about the 91st percentile for their age, even though they would answer very different numbers of items.
How raw abilities change across the lifespan
Different abilities follow different curves. In a study of nearly 50,000 online participants plus standardisation data, Hartshorne and Germine (2015) found that processing speed peaked around the late teens, some memory abilities in the 20s and 30s, and vocabulary not until the late 60s or early 70s. Salthouse (2009) reported that declines in some reasoning and speed measures can be detected from early adulthood, while knowledge-based measures keep rising for decades.
Psychologists often summarise this as a contrast between fluid abilities (novel problem-solving and speed, which peak earlier) and crystallised abilities (knowledge and vocabulary, which accumulate). Because IQ is age-normed, these trends do not show up as falling IQ scores; they show up in the raw scores behind the norms.
Is a child’s IQ stable?
Scores before school age are noticeably less stable, which is why psychologists treat preschool IQ results as provisional. From late childhood onward, rank order is remarkably consistent. In the follow-up of the 1932 Scottish Mental Survey, scores on the same test taken at age 11 and again at about 77 correlated .63 (about .73 after correcting for range restriction) (Deary et al., 2000). That is high stability — and also clear evidence that individuals can move substantially over a lifetime.
Can IQ change in adulthood?
Individual scores can shift by several points between testings because of measurement error, practice effects, health, sleep, mood or education. Education in particular appears to raise measured ability. Large, lasting gains from “brain training” apps have not been convincingly demonstrated. In older age, illness and medication can lower scores, which is one reason sudden declines warrant a medical check.
Age, norms and the Flynn effect
Norms are also tied to a calendar year. Average raw performance rose by roughly 3 points per decade during much of the 20th century (Trahan et al., 2014), with gains slowing or reversing in some countries in recent decades (Bratsberg & Rogeberg, 2018). Comparing an older adult with a younger one on the same raw score therefore mixes ageing with generational change. Age-specific, recent norms avoid both problems.
Mental age vs. IQ
Early tests used a ratio IQ: mental age divided by chronological age, times 100. A 10-year-old performing like a typical 12-year-old had a ratio IQ of 120. That formula breaks down for adults (raw ability does not keep rising every year), so modern tests use deviation IQ instead. Online claims of very high childhood IQs often come from ratio-IQ calculations that are not comparable to today’s scores.
Sources
- Wechsler, D. (2008). WAIS-IV Technical and Interpretive Manual. Pearson. (Descriptive classifications; FSIQ range 40–160; normative sample N = 2,200, ages 16–90.)
- Wechsler, D. (2014). WISC-V Technical and Interpretive Manual. Pearson. (Descriptors Extremely High … Extremely Low.)
- Hartshorne, J. K., & Germine, L. T. (2015). When does cognitive functioning peak? Psychological Science, 26(4), 433–443.
- Salthouse, T. A. (2009). When does age-related cognitive decline begin? Neurobiology of Aging, 30(4), 507–514.
- 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.
- Trahan, L. H., Stuebing, K. K., Fletcher, J. M., & Hiscock, M. (2014). The Flynn effect: A meta-analysis. Psychological Bulletin, 140(5), 1332–1360.
- Bratsberg, B., & Rogeberg, O. (2018). Flynn effect and its reversal are both environmentally caused. PNAS, 115(26), 6674–6678.
- Terman, L. M. (1916). The Measurement of Intelligence. Houghton Mifflin.
Frequently asked questions
What is the average IQ by age?
100 at every age. IQ tests are normed separately for each age group, so the typical person of any age scores 100.
What is the average IQ for a 13-year-old?
100. A 13-year-old is compared with other 13-year-olds on age-specific norms (for example WISC-V).
Does IQ go down with age?
IQ (age-normed) does not systematically fall, but raw abilities such as processing speed decline from early adulthood, while vocabulary and knowledge keep rising into the 60s.
Is a child’s IQ score permanent?
No. Scores before school age are less stable; from late childhood rank order is fairly stable (age-11 to age-77 correlation about .63 in Scottish data), but individuals can change.
At what age is intelligence highest?
It depends on the ability: processing speed peaks around the late teens, some memory skills in the 20s–30s, and vocabulary around the late 60s.