When Does IQ Peak? At Age 20 It Probably Stops Increasing - PsyBlog (2024)

IQ peaks and stops increasing at around 20 years of age and then is mostly fixed for life.

IQ peaks at around 20-years-old and later effort will not improve it much beyond this point, research finds.

The complexity of people’s jobs, higher education, socialising and reading all probably have little effect on peak cognitive ability.

Naturally, these activities have many other benefits, but little influence on intelligence.

However, education is particularly important at an early age when the brain is still developing.

By early adulthood, though, most people’s IQ has settled down.

When IQ is fixed

IQ can increase by as much as 20 points in only four years across the early to late teens, research finds (Ramsdenet al., 2011).

During this time young people’s IQ shifts dramatically both up and down.

For the study, 33 adolescents were followed over four years.

MsSue Ramsden, the study’s first author, explained the results:

“We found a considerable amount of change in how our subjects performed on the IQ tests in 2008 compared to four years earlier.

Some subjects performed markedly better but some performed considerably worse.

We found a clear correlation between this change in performance and changes in the structure of their brains and so can say with some certainty that these changes in IQ are real.”

Can IQ be increased after this peak?

However, while some studies have suggested that cognitive activities in later life can improve IQ, Professor William S. Kremen, author of one study on the subject, thinks otherwise:

“The findings suggest that the impact of education, occupational complexity and engagement in cognitive activities on later life cognitive function likely reflects reverse causation.

In other words, they are largely downstream effects of young adult intellectual capacity.”

The study included 1,009 men now in their 50s and 60s whose IQ was assessed when they were around 20-years-old.

They were given tests of abstract reasoning, verbal fluency and memory, among with other cognitive measures.

The results showed that most of the difference between the men’s IQs in mid-life was explained by the difference between them at around 20-years-old.

In comparison, the complexity of the job they had, the intellectual activities they engaged in, and their education in the meantime hardly had any effect on their peak IQ.

Brain scans also showed that IQ at age 20 was associated with the surface area of the cerebral cortex.

The cerebral cortex is the brain’s gray matter, the part that performs the higher functions of thinking, perceiving and language.

Most of the benefits of education for peak IQ likely happen before young adulthood, said Professor Kremen:

“Our findings suggest we should look at this from a lifespan perspective.

Enhancing cognitive reserve and reducing later life cognitive decline may really need to begin with more access to quality childhood and adolescent education.”

Maybe IQ does not stop increasing

Not everyone agrees, though, that IQ is fixed, since there is increasing evidence of brain plasticity at later ages.

Perhaps IQ and can peak later and higher?

Professor Cathy Price, who co-authored the study with Ms Sue Ramsden, said:

“The question is, if our brain structure can change throughout our adult lives, can our IQ also change?

My guess is yes.

There is plenty of evidence to suggest that our brains can adapt and their structure changes, even in adulthood.”

The study was published in the journal PNAS (Kremen et al., 2019).