Average IQ by Age: Why It’s 100 for Kids, Teens and Adults

You search “average IQ by age” expecting a neat chart: one number for 8-year-olds, another for teens, another for adults. Plenty of sites will give you one. The catch is that standard IQ tests are built so that this chart has only one number in it, and understanding why tells you far more about your own score (or your child’s) than any made-up table.

Average IQ by age: why the answer is always 100

An IQ score is not a count of how many questions you got right. It is a comparison. When a test publisher builds a test, it gives the questions to a large “norm sample” of people at every age the test covers, then converts raw scores into a scale where the average for each age group is 100 and the standard deviation is 15.

The big clinical tests are explicit about this. Pearson’s WISC-V, a leading children’s IQ test in the US, was standardized on 2,200 children aged 6 to 16, and its scores are described “relative to same-age peers.” The adult version, the WAIS-IV, was normed on 2,200 people split into 13 separate age bands from 16 to 90, according to Pearson’s WAIS-IV brochure.

That design has a simple consequence. Suppose an 8-year-old and a 15-year-old take the same children’s test. The 15-year-old will almost certainly answer more questions correctly. But if each answers exactly as many as the typical child their age, both get an IQ of 100. The average IQ by age is 100 because the scoring makes it so.

Where the “IQ goes up with age” idea comes from

The confusion is understandable, because the very first IQ formula really did work with age. In 1912 the German psychologist William Stern proposed dividing a child’s “mental age” by their actual age, and Lewis Terman later multiplied the result by 100. As the Mensa International explainer on IQ puts it, the equation became mental age divided by chronological age, times 100.

That ratio IQ worked tolerably for children and fell apart for adults. Raw reasoning ability levels off in early adulthood, but your birthday keeps arriving every year, so a perfectly ordinary 40-year-old would have seemed to lose IQ points simply by aging. That is why modern tests switched to the deviation IQ: compare each person with their own age group and place them on a bell curve. Our guide to what IQ is and how it is calculated walks through both formulas with worked examples.

Many “average IQ by age” charts online still list a different average for each age group, often with no test, norm sample or year attached. On any modern, age-normed test, those numbers don’t reflect how scoring works.

Average IQ score by age: the chart

This is the honest version of the chart people are searching for. The middle columns are the same in every row on purpose. What differs is which test is used and what is happening to raw ability at that stage of life.

A few details behind the table. The WPPSI-IV covers children from 2 years 6 months to 7 years 7 months. The Stanford-Binet Fifth Edition spans ages 2 to 85+ and was normed on 4,800 people. The newest adult Wechsler scale, the WAIS-5, was published in 2024 and covers ages 16:0 to 90:11. Because the WISC-V and the adult scales overlap at age 16, a 16-year-old may take either one, depending on the psychologist’s judgment.

IQ score chart by age: what each score means at any age

Since every age group is placed on the same curve, the IQ range by age looks identical whether you are 9 or 59. The table below shows what common scores mean, regardless of age.

So about 68% of any age group lands between 85 and 115, and about 95% between 70 and 130. For every range, classification and percentile in one place, see the full IQ scale and chart; for what counts as a strong result, see our guide to what counts as a good IQ score. For why scores spread out in a bell shape, and why the extremes are hard to measure, read the IQ bell curve explained.

What actually changes with age: raw cognitive ability

If IQ stays centered on 100, does anything really change as you age? Yes, a lot. It just shows up in raw performance rather than in the IQ number.

The clearest picture comes from a 2015 study in Psychological Science by Joshua Hartshorne and Laura Germine (full text on PubMed Central). They combined normative data from standardized IQ and memory tests with results from 48,537 online participants and found “considerable heterogeneity in when cognitive abilities peak”:

• Processing speed (the digit-symbol coding task) peaked in the late teens.
• Short-term memory for digits peaked in the early twenties.
• Working memory peaked around 30.
• Emotion recognition peaked later, with a broad plateau between about 40 and 60.
• Vocabulary peaked around 50 in the WAIS-III norms and around 65 in the online data.

The authors concluded that there may be no single age at which people are at their peak on most cognitive tasks. Psychologists often summarize this as fluid intelligence (reasoning with new problems, speed) peaking early, while crystallized intelligence (knowledge, vocabulary) keeps growing.

Timothy Salthouse’s long-running Virginia study points the same way. In a 2009 paper in Neurobiology of Aging (Salthouse, full text on PubMed Central) covering 2,350 adults aged 18 to 60, he concluded that some aspects of age-related decline begin in healthy, educated adults in their 20s and 30s, while measures of accumulated knowledge “are consistently found to increase until at least age 60.” The exact timing of early decline is still debated among aging researchers, but the broad pattern (speed early, knowledge late) is well established.

Average IQ for 12, 13, 14 and 15 year olds

The direct answer for early teens: the average IQ for a 12-year-old, a 13-year-old, a 14-year-old and a 15-year-old is 100 in every case. The typical range is also the same, with about two-thirds of each age scoring between 85 and 115.

What is different about the early teen years is the test and the stability of the score:

1. Which test is used. Clinical testing at 12 to 15 is usually done with the WISC-V, which covers ages 6:0 to 16:11. Adult scales like the WAIS start at 16.
2. How much scores move. A 2024 meta-analysis in Psychological Bulletin by Breit, Scherrer, Tucker-Drob and Preckel found that stability is low in preschoolers, rises quickly through childhood and stays high from late adolescence on. A teen’s score is more meaningful than a 5-year-old’s, but it can still shift.
3. Raw growth is still happening. A 15-year-old answers more questions correctly than a 12-year-old, but each is compared with peers who are growing too.

An IQ of 115 at 13 means the same thing as 115 at 40: higher than about 84% of people that age. If you are wondering whether a child might be gifted, scores are only one piece of the picture. Our guide to the signs of a gifted child covers what schools actually look for. Any decision about a child’s schooling or support should go through a school psychologist or a licensed psychologist, not an online test.

Average adult IQ, and does it drop as you get older?

The average adult IQ is 100, from age 16 to 90. That holds even though older adults, on average, answer fewer speed-based items correctly than younger adults. The adult Wechsler scales handle this by scoring you within your own age band: the WAIS-IV, for example, uses 13 age bands from 16 to 90. A 75-year-old who scores 100 is exactly average for 75-year-olds.

There is one more reason the average stays at 100: tests are re-normed. Across the 20th century, raw scores on IQ tests rose by roughly 3 points per decade, the so-called Flynn effect, explained in our guide to the IQ bell curve and percentiles.

That is why publishers release new editions with fresh norms, like the WAIS-5 in 2024. If a test with decades-old norms is used, people can look “above average” simply because the comparison group is out of date.

How stable is IQ from childhood to adulthood?

Knowing that the average is 100 at every age leads to the next question: does a person keep roughly the same position on the curve? Mostly, yes, once childhood is over.

The 2024 Psychological Bulletin meta-analysis pooled 205 longitudinal studies with 87,408 participants. For a 20-year-old retested five years later, the average rank-order correlation was 0.76. In children, stability reaches the 0.80 level needed for individual diagnostic decisions only after about age 7, and only over short retest intervals. General intelligence was the most stable ability they examined.

The most striking long-range evidence comes from Scotland. In the Lothian Birth Cohort of 1921, 106 people took the same intelligence test, the Moray House Test, at age 11 and again at age 90. Their scores correlated at 0.54, or 0.67 after a statistical correction, as reported in Psychological Science in 2013 by Ian Deary and colleagues. That is substantial stability across almost 80 years, and also plenty of room for individuals to move.

Find out where you stand for your age

Averages are useful context, but the question most people really have is where they land among people their age. That takes a measured score, not a chart.

You can take the IQtonics IQ test: 40 questions across patterns, spatial reasoning, numbers, logic and memory, with a 20-minute time limit. Questions get harder as you go, and harder ones carry more points. Your result is reported on the same scale used throughout this article (mean 100, standard deviation 15; our methodology page explains how it is scored) with a percentile, plus a cognitive profile showing your strengths, best area and areas to improve.

Starting the test is free; your full results unlock with a trial membership, which renews automatically unless you cancel. It is an online test, not a clinical assessment, so treat it as an informed estimate, and if you are curious how online tests compare with clinical ones, read are online IQ tests accurate.