The average adult IQ is actually lower than you might think!

What Is the average adult IQ?

The average adult IQ is actually lower than you might think! There are many factors that affect your IQ, including age, environment, and nutrition. 

Still, there are a lot of myths surrounding IQ scores, so it’s important to understand the science behind intelligence and how to increase your score if you feel it’s lacking. Read on to find out more about what the average IQ for adults really is and how to improve your own!


Most people assume that the average adult IQ hovers around 120, with IQ scores continuing to rise as we age. However, that’s not always the case. In fact, one study showed that the average adult IQ actually falls from 95 at age 18 to 90 at age 65!


In the United States, the average IQ for adults has been found to be 98. The distribution of IQ scores in adults finds that around 68% of adults have an IQ between 85 and 115, while only a small number of people have a very low IQ (considered 70 or below) or an incredibly high IQ (scores above 130).

Average Adult IQ

How different are adult IQs?

This distribution of scores when measuring the IQ of adults is known as the bell shaped curve, which is a common type of distribution, known as the normal distribution.

When IQ scores are plotted on a graph, they typically follow a bell-shaped curve. The peak of the “bell” occurs where the majority of the scores lie. The bell then slopes down to each side; one side represents lower than average scores and the other side represents scores that are above the average.

A number of standardised IQ tests have been developed over the years to help determine an Individual’s IQ score, and measure against a base line, or collective score, from measuring a large number of other people.

The majority of these tests have found that an average IQ score is between 90 and 109. Below are some examples of the different ‘levels’ of IQ score, and where they place the individual when compared to their peers in a normal distribution such as the bell-shaped curve.


  • IQ score of 130 and above: Very Superior
  • IQ score of 120-129: Superior
  • IQ score of 110-119: High Average
  • IQ score of 90-109: Average
  • IQ score of 80-89: Low Average
  • IQ score of 70-79: Borderline
  • IQ score of 69 and below: Extremely low
Average Adult IQ

What factors influence an adult's IQ?

So, what factors might influence whether a person has an average IQ as an adult, or an IQ below or above this average?

Well, lots! And many are most influential during childhood. A study found that environmental factors such as place of residence, the physical activity of a child, the family income, and parental education level have an important impact on the IQ of the children (Makharia, 2016).

But genetics also plays a key role in determining whether an adult has an average IQ. Studies of identical twins have found a correlation between intelligence and genetics, with identical twins IQ scores more similar than those of fraternal twins. This shows that siblings with a more similar genetic makeup are more likely to report similar IQ scores, and thus cement the notion of genetic factors in IQ. Other studies have found that siblings raised together in the same environment had more similar IQ scores than adopted children raised alongisde them, suggesting that although all children shared a similar environment, genetic similarities between siblings meant there was a greater correlation between their IQ scores.

But as well as environmental and genetic factors, biological factors influencing foetal development can also have an impact on whether a child grows up to have an average IQ as an adult. These include exposure to drugs and harmful substances in the womb, the age of the mother, and whether the baby received all the necessary nutrients in the womb, or suffered from prenatal malnutrition.

Average Adult IQ