What Is the Average IQ by Age?

By the IQScore Fun team

Type "average IQ by age" into a search bar and you'll find plenty of tables promising a neat number for every birthday. Ten-year-olds get one score, thirty-year-olds get another, seventy-year-olds get a lower one. It looks tidy. It's also a bit misleading, so let's straighten it out.

The short answer is that the average IQ is 100 at every age. Always. That isn't a coincidence or a happy accident. It's how the scale is built.

IQ is a comparison, not a measurement

An IQ score doesn't tell you how much you know, or how many puzzles you can solve in some absolute sense. It tells you how your performance compares with other people of your own age. When a publisher builds an IQ test, it gives the test to a big, carefully chosen sample of people in different age groups. Then the scoring is set so the middle of each age group lands on 100.

On most major tests the spread works out like this: about two out of three people in any age group score between 85 and 115, and roughly 95 out of 100 score between 70 and 130. That's true for kids, for twenty-somethings and for retirees.

So a 10-year-old with an IQ of 100 is average for ten-year-olds. A 70-year-old with an IQ of 100 is average for people in their seventies. Neither one is "smarter" than the other in any raw sense. Each has been compared with their own peers, and that's the whole point.

Where the old "mental age" idea came from

The earliest IQ tests worked differently. Back in the early 1900s, the idea was to work out a child's "mental age" and divide it by their real age, then multiply by 100. If an eight-year-old performed like the typical ten-year-old, the math gave 10 divided by 8, times 100, which is 125.

For children, that formula was workable, because kids' abilities grow quickly from year to year. For adults it falls apart. Nobody's mental age keeps climbing in the same way after their twenties. Run the formula on a 60-year-old who performs like a typical 30-year-old and you'd get an IQ of 50, which is obviously absurd.

That's why modern tests dropped the ratio and switched to what's called a deviation IQ. In plain terms, your raw score is turned into a position within your age group, and that position is translated onto the familiar scale with 100 in the middle. The "mental age" language stuck around in popular culture, but it isn't how real scores are calculated today.

So what actually changes with age?

Your IQ score, if you could take the same test at different ages, would tend to stay in a similar neighborhood. But the abilities underneath it don't all move together. Psychologists often split thinking skills into two broad groups.

This is why an older person might lose a race against a teenager on a timed pattern puzzle and still beat them easily at a vocabulary quiz or at making a sensible decision about money. Neither result means one of them has a "higher IQ" overall. Different tasks lean on different abilities, and those abilities follow different curves over a lifetime.

It's also worth saying that the decline in fluid reasoning is gradual, and it varies a lot from person to person. Staying mentally active, sleeping properly, exercising and keeping up social contact all seem to help. Nobody wakes up on their 31st birthday suddenly slower.

Children's scores move around more

If you've got a young child and you're wondering what their "IQ" means, one thing is worth knowing. Scores in early childhood are less stable than scores later on. Little kids are growing and learning fast, they have off days, and they don't always cooperate with a test that wants them to sit still for an hour. Psychologists tend to treat scores from very young children with extra caution, and scores generally become more stable by the school years and adolescence, though even then they're not carved in stone.

So if a child scores lower than you hoped on a test, that isn't a prediction of their future. And if they score higher, it isn't a guarantee either.

The Flynn effect, and why tests get updated

Here's a strange fact that explains a lot. For much of the twentieth century, raw scores on IQ tests rose in many countries, by roughly three points per decade according to the often-cited estimates. This is called the Flynn effect, after the researcher who documented it. In some countries, more recent data suggest the rise has flattened or even reversed, so the picture isn't uniform.

What matters for our topic is the consequence. If people keep scoring higher on the same questions, an old test would make the average person look like they have an IQ above 100. To keep 100 as the true average, test publishers re-norm their tests every so often, using fresh samples of people. It's another reminder that IQ is always relative to a reference group, not a fixed yardstick.

What this means for the IQScore Fun test

Let's be upfront about our own test. It's a short, 20-question practice test and it does not adjust your score for age. It gives one estimate based on how many questions you got right. That makes it fine for fun and for practice, but it can't tell you where you stand compared with other people your age. A real, professionally normed test can.

If you're a teenager or an older adult taking our test, treat the result as a snapshot of how you did on these particular puzzles, not as a statement about your intelligence.

The takeaway

If you came here looking for a table of "average IQ for a 15-year-old" versus "average IQ for a 45-year-old," the honest answer is that they're both 100. What changes with age isn't the average score, it's the mix of skills behind it. And the best use of any IQ number is as one small piece of information, not as a label.

Curious how you do on number, logic and pattern puzzles? You can try the free test, or read our guide to the IQ score chart to see what different scores mean.