Search for "average IQ by age" and you'll find charts claiming a typical 10-year-old has an IQ of 70, or that scores drop steadily after 30. They look scientific. They're also built on a misunderstanding of how IQ scores work.
Here's the surprise: on any properly normed test, the average IQ is 100 at every age, from childhood to your eighties. That isn't because thinking stays the same across life. It's because of how the score is calculated. Once you see that, the interesting question becomes what actually changes as you age, and the answer is more encouraging than most people expect.
The short answer: 100, at every age
Modern IQ tests compare you with people your own age. A 12-year-old is compared with other 12-year-olds, and a 70-year-old with other 70-year-olds. Within each age group, the average is set to 100 and the standard deviation to 15.
So the average IQ for a 20-year-old is 100. The average for a 50-year-old is 100. The average for an 80-year-old is also 100. If you'd like a refresher on how the bell curve and percentiles fit together, our guide to what counts as a good IQ score walks through it.
| Age group | Average IQ score | What raw ability is doing |
|---|---|---|
| Young children | 100 | Rising very quickly year to year |
| Teenagers | 100 | Still rising, especially reasoning speed |
| Early adulthood | 100 | Fluid reasoning near its peak |
| Middle age | 100 | Knowledge still growing, speed easing slightly |
| Later life | 100 | Knowledge often stable, speed and new-problem solving declining |
The left column stays fixed. The right column is where life happens.
Why IQ didn't always work this way
The earliest intelligence scores really did depend on age in a different way. In the early 1900s, the psychologist William Stern proposed comparing a child's "mental age," the level they performed at, with their actual age. Lewis Terman later multiplied that ratio by 100 for the Stanford-Binet test.
So a 10-year-old performing like a typical 12-year-old would score 120. This ratio IQ worked reasonably for children, but it fell apart for adults. Mental age doesn't keep climbing every year after your teens, so the formula would make everyone look less intelligent as they aged.
David Wechsler's adult tests, starting in the late 1930s, solved this with the deviation IQ: compare people with their own age group and express the result on a fixed scale. That is the system nearly every modern test uses.
What actually changes with age
Under the hood, your raw performance on different kinds of tasks does shift across life. Psychologists often split intelligence into two broad types.
Fluid intelligence
This is the ability to reason with new problems, spot patterns and think quickly. On average, it rises through childhood and adolescence, peaks in early adulthood and declines gradually from there. Processing speed, in particular, tends to peak early.
Crystallised intelligence
This is the knowledge and skills you've built up: vocabulary, general knowledge, expertise. It often keeps growing well into middle age and stays fairly stable for many people into later life.
A large 2015 study by Joshua Hartshorne and Laura Germine, using data from many thousands of people online, found that different abilities peak at very different ages, with some processing tasks peaking in the late teens and vocabulary peaking decades later. Our post on fluid vs crystallised intelligence explains the difference in more detail.
Does your IQ score change as you age?
Because scores are compared with your age group, your IQ tends to be quite stable in adulthood, even while your raw abilities shift. If everyone your age slows down by a similar amount, your relative position stays about the same.
Some of the most striking evidence comes from Scotland. In 1932, almost every 11-year-old in the country sat the same mental ability test. Decades later, researchers led by Ian Deary retested some of those people in their late 70s and beyond. Their childhood and later-life scores were fairly strongly correlated, showing that rank order is surprisingly persistent across a lifetime.
Stable doesn't mean fixed, though. Scores in early childhood are much less stable than adult scores, and education, health and life experience can all move a person's relative position.
Why "average IQ by age" charts mislead people
Charts showing IQ falling with age usually make one of these mistakes:
- They mix up raw scores and IQ scores. Raw performance on speed tasks does decline with age. IQ, which is age-normed, doesn't drop on average.
- They use old ratio-IQ logic. Applying mental-age formulas to adults makes scores look like they collapse after the teens.
- They compare different generations. Older generations took tests under different conditions and schooling, which brings in the Flynn effect.
- They rely on unrepresentative samples. Online quiz data often over-represents certain groups, making comparisons unreliable.
The generation problem: the Flynn effect
During much of the 20th century, raw scores on IQ tests rose in many countries by roughly three points per decade, a pattern named after researcher James Flynn. This means a test normed decades ago becomes "easier" over time, so test publishers regularly update their norms.
It also means that cross-sectional studies, which compare today's 20-year-olds with today's 70-year-olds at the same moment, can exaggerate age decline. Part of the gap reflects generational differences in schooling and environment rather than ageing alone. We explain the full story in the Flynn effect.
How to read your own score fairly
When you take a test, keep these points in mind:
- Your score is relative to your age group. A 100 at 65 and a 100 at 25 both mean "typical for your age."
- Raw speed matters less than you think. Slowing down on timed puzzles is normal and doesn't erase knowledge or judgement.
- Look at the range, not the point. Every test has measurement error, so think in bands of several points.
- Consider the test's norms. A well-built test should be normed on a broad, recent sample.
If you want to see how you compare with others, take our free IQ test and treat the result as a snapshot of your current reasoning, not a permanent label.
Can you slow age-related decline?
Research on cognitive ageing points to ordinary but meaningful habits. Staying physically active, keeping socially connected, sleeping well, managing blood pressure and continuing to learn new things are all linked with healthier thinking in later life. None of them guarantees a particular score, but together they support the brain you have.
The bottom line
The average IQ is 100 at every age, because tests compare you with your own age group. What changes over a lifetime is raw ability: fluid reasoning and speed peak early and ease off, while knowledge often keeps growing for decades. So if you see a chart claiming IQ collapses after 30, it's measuring something else.
FAQ
What is the average IQ for a 30-year-old?
It's 100, the same as for any other age. IQ tests are normed so that the average within each age group is always 100.
Does IQ go down as you get older?
Your IQ score tends to stay fairly stable because it's compared with people your age. Raw abilities like processing speed do decline gradually, while knowledge often holds steady or grows.
At what age is IQ most stable?
Scores become much more stable from late childhood and adolescence onward. Early childhood scores are less predictive of later results.
