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Feb 11, 2026·Average IQ & Demographics

What Is the Average IQ by Age?

The average IQ is 100 at every age. Learn age-based norming, which compares you to your peers, and why cognitive abilities like processing speed decline over time.

Dr. Russell T. WarneChief Scientist
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What Is the Average IQ by Age?
The average IQ is 100 at every age. This is not because cognitive abilities remain constant throughout life, but because IQ tests use age-based norming that compares individuals only to others of the same age, and the average is always arbitrarily set to 100. Understanding this scoring system clarifies why the average is always 100 and what actually changes cognitively across the lifespan.

Why Is the Average IQ 100 at Every Age?

IQ tests are deliberately constructed so that 100 represents the average score for any age group. When test developers create a new IQ test, they administer it to a large, representative sample of the population that includes people of different ages. The average raw performance for each age group is then mathematically transformed to equal an IQ of 100, with scores distributed around this average according to a standard deviation of 15 points.

This standardization process, called norming, ensures that IQ scores reflect relative standing within an age group rather than absolute cognitive capacity. A 25-year-old who scores 100 performed at the average level for 25-year-olds, while a 70-year-old who scores 100 performed at the average level for 70-year-olds. This approach allows meaningful comparison of individuals across different ages using the same metric. It also accounts for normal developmental changes without penalizing older adults for age-related cognitive slowing or crediting young adults simply for being at their cognitive peak.  

How Do Raw Cognitive Abilities Change with Age?

While standardized IQ scores remain anchored at 100 for each age group, the raw cognitive abilities underlying those scores change substantially across the lifespan. Research on cognitive aging has documented distinct trajectories for different types of cognitive abilities.

Fluid intelligence, or the capacity for reasoning, problem-solving, and processing novel information without relying on prior knowledge, follows an inverted U-shaped curve. These abilities develop rapidly during childhood, peak in late adolescence or early adulthood (typically between ages 18 and 25), and then gradually decline throughout the remaining lifespan. Processing speed and working memory show particularly pronounced age-related declines, with noticeable changes beginning in the 30s and continuing into old age.

Crystallized intelligence follows a markedly different pattern. These abilities continue developing through early and middle adulthood as individuals acquire more knowledge and expertise. Crystallized abilities remain relatively stable well into the 60s and 70s, declining only in very late life when health conditions may intervene.

This divergence between fluid and crystallized abilities explains why age-based norming is essential. Without it, young adults would consistently outscore older adults on IQ tests emphasizing fluid reasoning, not because they are more intelligent in any meaningful sense but because the raw abilities being measured happen to favor youth.  

When Do Different Cognitive Abilities Peak?

Different cognitive abilities reach their maximum levels at different ages, creating a complex picture of cognitive development rather than a single "peak" age for intelligence. Processing speed, or the ability to complete simple cognitive tasks quickly and accurately, peaks earliest, typically in the late teens or early 20s. This is when reaction times are fastest and mental operations are most efficient. Declines begin relatively early and continue steadily throughout adulthood.

Working memory, or the capacity to hold and manipulate information temporarily, peaks somewhat later, typically in the mid-20s. This ability supports complex reasoning, mental arithmetic, and following multi-step instructions. Declines are gradual but become noticeable by middle age. Fluid reasoning, or the ability to solve novel problems, identify patterns, and think abstractly, peaks in the early to mid-20s for most individuals. This is the classic "raw intelligence" that allows tackling unfamiliar challenges without relying on prior knowledge. The decline is gradual, with most individuals retaining substantial fluid reasoning capacity well into later life despite measurable decreases.

Verbal abilities and general knowledge continue to develop through the 40s and 50s for many individuals. Vocabulary knowledge, in particular, shows remarkable stability, often remaining at peak levels until the 70s or beyond in healthy adults. This explains why older adults often excel in domains requiring accumulated expertise even as their processing speed slows. Spatial ability follows a trajectory similar to fluid reasoning, peaking in early adulthood and showing a gradual decline thereafter. However, substantial individual variation exists, and some individuals maintain strong spatial abilities well into later life.

What Happens to IQ Test Performance in Childhood?

During childhood and adolescence, cognitive abilities develop rapidly. A 10-year-old possesses substantially greater cognitive capacity than a 5-year-old, who in turn far exceeds a 2-year-old. These developmental changes are dramatic and obvious to any observer. IQ tests for children account for this development through age-based norming. A child's raw score is compared only to other children of the same age, producing a deviation IQ indicating relative standing within their age group. A 7-year-old with an IQ of 115 performed better than approximately 84% of other 7-year-olds, not better than 84% of the general population, including adults.

The original IQ formula of mental age divided by chronological age, multiplied by 100, captured this developmental perspective differently. A child performing at the level typical of older children received a higher IQ, while one performing at the level typical of younger children received a lower IQ. This "quotient IQ" approach has been replaced by deviation IQ scoring but reflects the same underlying insight: children's cognitive abilities develop predictably with age, and meaningful assessment requires accounting for developmental stage.

IQ scores show moderate stability during childhood, with correlations between scores at different ages typically ranging from .30 to .80, depending on the time interval and ages involved. Stability increases with age, and scores become highly stable by late adolescence. For more on testing children, see our article on IQ tests for kids.

What Happens to IQ Test Performance in Adulthood?

Once cognitive development largely completes in early adulthood, IQ scores become remarkably stable. An individual's relative standing compared to age-matched peers typically remains consistent over decades, with test-retest correlations often exceeding .80 (on a scale of 0 to 1).

This stability reflects several factors. The genetic contribution to cognitive ability differences is substantial and increases across the lifespan, reaching approximately 60-80% in adulthood. Once the developmental period ends, the factors maintaining individual differences remain relatively constant. Someone who scores at the 75th percentile among 30-year-olds will likely score near the 75th percentile among 50-year-olds and 70-year-olds as well when they reach those ages. However, the raw abilities underlying these stable percentile rankings do change. The age-based norming process accounts for expected declines, comparing older adults only to other older adults experiencing similar changes. This is why a 75-year-old can receive the same IQ score as they did at age 25, despite measurably slower processing speed. Their relative standing within their age group has remained constant.

Pathological conditions represent exceptions to this stability. Dementia produces a genuine cognitive decline that exceeds normal aging and would be reflected in declining IQ scores relative to age-based norms. Traumatic brain injury, stroke, and certain psychiatric conditions can similarly impair cognitive functioning in ways that depart from typical aging trajectories.

How Does the Flynn Effect Relate to Average IQ by Age?

The Flynn effect, which is the documented tendency for average IQ test performance to rise over successive generations, adds complexity to understanding average IQ by age. This phenomenon, named after researcher James Flynn, shows that populations have scored progressively higher on IQ tests throughout the 20th century, with gains averaging approximately 3 points per decade. The Flynn effect means that IQ norms become outdated over time. A test normed 20 years ago will produce inflated scores today because the current population performs better than the older norming sample. This is why legitimate IQ tests undergo periodic re-norming to maintain accuracy.

The Flynn effect does not mean that each generation is genuinely more intelligent than the previous one. Research indicates that the gains primarily reflect changes in the non-g abilities that IQ tests measure (improvements in test-taking familiarity, educational exposure to abstract reasoning, and other environmental factors) rather than increases in core general intelligence. The gains have been largest on tests of fluid reasoning and smallest on tests of crystallized knowledge. In some countries, the Flynn effect has slowed, stopped, or even reversed in recent decades. This likely reflects changes in educational curricula and the degree to which schooling emphasizes the skills that IQ tests measure. For more on this phenomenon, see our article on the Flynn effect.

Do Average IQ Scores Differ Across Age Groups Today?

When IQ tests are properly normed, the average score is 100 for every age group by definition. However, examining raw score patterns before age adjustment reveals the underlying cognitive differences across age groups.

Young adults (ages 18-25) typically achieve the highest raw scores on tasks measuring fluid reasoning, processing speed, and working memory. If these scores were compared to a single overall norm rather than age-specific norms, young adults would appear to have the highest average IQ.

Middle-aged adults (ages 40-60) show lower raw performance on fluid tasks but maintain or exceed young adult levels on crystallized tasks. Their overall raw performance depends heavily on the specific mix of subtests a given IQ test includes.

Older adults (ages 65+) show the largest declines in processing speed and fluid reasoning but often maintain strong performance on vocabulary and knowledge-based tasks. The pattern varies considerably by individual health status, education, and lifestyle factors.

These patterns explain why comprehensive IQ tests measure multiple cognitive abilities rather than relying on a single task type. A test emphasizing only processing speed would systematically favor young adults, while one emphasizing only vocabulary would favor middle-aged and older adults. By sampling across ability domains, well-designed tests provide balanced assessment across the age range.

How Should Adults Interpret Their IQ Scores?

Understanding that IQ scores reflect age-adjusted comparisons helps adults interpret their results appropriately. A score of 115 at age 60 indicates performance exceeding approximately 84% of other 60-year-olds, which is a meaningful achievement that accounts for normal aging. Additionally, adults should not compare their current scores to what they might have achieved at younger ages and interpret any difference as a decline. The age-based norming system is specifically designed to prevent such misleading comparisons. What matters is standing relative to age-matched peers, which typically remains stable throughout adulthood.

Comprehensive IQ tests provide cognitive profiles showing performance across multiple ability domains. These profiles may reveal that crystallized abilities have strengthened with age even as processing speed has slowed, which is a common and normal pattern that single IQ scores obscure. 

The Reasoning and Intelligence Online Test (RIOT) uses age-based norming to provide an accurate assessment for adults across the lifespan. Developed by Dr. Russell T. Warne, who has over 15 years of experience in intelligence research, the RIOT measures six cognitive abilities (verbal reasoning, fluid reasoning, spatial ability, working memory, processing speed, and reaction time), providing detailed profiles that reveal patterns of strengths and weaknesses. This comprehensive approach, combined with proper age-based norming, ensures that scores meaningfully reflect cognitive standing regardless of the examinee's age.

Watch “How Intelligence and IQ Work in the Brain” with Dr. Richard Haier on the Riot IQ YouTube channel to see how age-related patterns in IQ are influenced by brain development and function.
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Dr. Russell T. WarneChief Scientist

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