Average IQ by age

Short answer: 100 at every age, because each age group is compared only with itself. The interesting part is what happens to the abilities behind the score.

Why the average is always 100

IQ tests are normed separately for each age group. A 10-year-old is compared with other 10-year-olds and a 70-year-old with other 70-year-olds. So the average IQ is 100 for every age, and a stable IQ means you are keeping pace with your peers.

Raw ability does change

Behind the scaled score, the number of problems people can solve rises quickly in childhood, peaks in early adulthood and slowly changes after that. Different abilities follow different paths.

Fluid versus crystallised

Fluid reasoning and processing speed, solving new problems quickly, peak around the twenties and decline gradually. Crystallised ability, vocabulary and knowledge, keeps growing into the sixties and holds up well into old age.

How to keep sharp

Physical exercise, good sleep, social contact, treating hearing loss and continued learning are all linked with slower cognitive decline. Brain-training games mostly improve the games themselves.

What changes at each age

Age	Average IQ	What changes in raw ability
6–11	100	Reasoning, vocabulary and memory grow quickly every year.
12–17	100	Abstract thinking and speed keep improving through the teens.
18–29	100	Fluid reasoning and processing speed are near their peak.
30–44	100	Knowledge keeps growing while speed starts to ease slightly.
45–64	100	Knowledge-based skills are often at their best; solving new problems slowly gets harder.
65+	100	Speed and working memory decline more, while vocabulary holds up well.

Trends are averages from research on large groups. Individuals vary widely.

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