Many people who took an IQ test as a child wonder whether that number still describes them decades later. The short answer is that two different things are going on at once. Your raw abilities do change across your life, some rising and some falling, while your IQ score, which compares you with people your own age, tends to stay surprisingly stable. Keeping those two ideas apart clears up most of the confusing claims about IQ and aging.
Does Your IQ Change as You Get Older?
Your IQ score usually stays fairly stable relative to people your age, but your underlying abilities do not stand still. Some, like processing speed, start declining in early adulthood, while others, like vocabulary, keep growing for decades.
Lifelong studies show both patterns clearly. Children tested at age 11 and retested at age 90 still ranked in a similar order, with a correlation of .54 between the two scores. At the same time, research on adults shows measurable drops in speed and reasoning that can begin as early as the late 20s, along with continued growth in knowledge. Whether IQ "changes" depends on whether you mean the score or the abilities behind it.
Why an IQ Score Can Stay the Same While Your Abilities Change
An IQ score is not an absolute measure. It shows where you rank compared with a reference group of people the same age, which psychologists call age norms. A 75-year-old with an IQ of 115 is compared with other 75-year-olds, not with 25-year-olds.
This creates two separate kinds of change that are easy to confuse. Rank-order stability is about whether you keep your relative position over time; mean-level change is about whether everyone's raw abilities rise or fall as a group. Raw speed can drop for an entire age group while each person's IQ, measured against that group, stays about the same. This is worth knowing before you take an IQ Test at any age: a well-normed result tells you how you compare with your peers right now, which is a different question from whether your mind works the way it did at 20.
How Stable Is IQ From Childhood to Old Age?
The strongest evidence comes from Scotland, where nearly a whole generation of children was tested at age 11. The Scottish Mental Survey of 1932 gave the Moray House Test, a 45-minute group intelligence test, to 87,498 children, about 95 percent of Scottish 10- and 11-year-olds that year.
Decades later, psychologist Ian Deary and colleagues at the University of Edinburgh traced survivors and gave them the same test again. Their early follow-ups found that when the same test was given at age 11 and again around age 80, about half of the variance in scores was stable. A 2013 study published in Psychological Science retested 106 members of the Lothian Birth Cohort of 1921 at age 90 and found a correlation of .54 with their age-11 scores, rising to .67 after a statistical correction for range restriction: the people still alive and able to take part at 90 varied less in ability than the original 1932 group.
Those numbers cut both ways. A correlation of .54 to .67 across 79 years is remarkably high: childhood ability still predicts a large share of where someone ranks at 90. But it is far from perfect: a correlation of that size leaves room for many individuals to move noticeably up or down relative to their peers over a lifetime.
Can IQ Change During the Teenage Years?
Yes, and by more than many people expect. A 2011 study published in Nature, led by neuroscientist Cathy Price at the Wellcome Trust Centre for Neuroimaging at University College London with first author Sue Ramsden, tested 33 healthy teenagers in 2004, at ages 12 to 16, and again four years later, at ages 15 to 20, with MRI brain scans at both points.
Some participants improved relative to their same-age peers by as much as 20 IQ points, and others declined by a similar amount. About 21 percent showed a significant change in verbal IQ, and about 18 percent moved up or down a level in nonverbal IQ. Only one participant changed significantly on both scales. The changes also lined up with the brain scans: that shifts in verbal IQ tracked structural changes in a brain region involved in speech production, and shifts in nonverbal IQ tracked changes in a region involved in finger movements. The sample was small, so the exact percentages should be read cautiously, but the study is a strong counterexample to the idea that a score at 13 locks in for life.
Which Abilities Decline With Age, and Which Keep Growing?
Different abilities follow different paths. Psychologist Timothy Salthouse of the University of Virginia tracked about 2,000 healthy adults aged 18 to 60 over seven years and published the results in the journal Neurobiology of Aging in 2009.
This split matches a long-standing distinction in intelligence research between fluid intelligence, the ability to reason through new problems quickly, and crystallized intelligence, the knowledge and skills built up through experience. Fluid abilities peak early and decline gradually; crystallized abilities keep accumulating well into middle age. An overall IQ score blends both kinds of ability, so a single number can hide opposite trends running underneath it.
The Case Against Early Cognitive Decline
Not every researcher accepts that decline starts in the 20s. Psychologist K. Warner Schaie, who led the Seattle Longitudinal Study at the University of Washington, published a direct response to Salthouse in the same journal in 2009, calling his conclusions unsupported.
Schaie's objection is methodological. Comparing people of different ages at one point in time, a cross-sectional design, mixes true aging effects with cohort differences: a 55-year-old and a 25-year-old grew up with different schooling and different exposure to test-like tasks, so a gap between them does not show how one person changes. Schaie argued that following the same people over time gives a different picture, with some abilities staying stable across roughly ages 20 to 60.
Both sides have a point. Cohort effects are real, as the large generational rise in test scores known as the Flynn effect shows. At the same time, Salthouse's data included repeated testing of the same individuals, not only cross-sectional comparisons. The fairest reading is that some decline in speed and novel reasoning begins in adulthood, but its timing and size depend heavily on how it is measured.
What These Studies Can't Tell You
They describe group averages and correlations. Any one person can follow a different path, as the teenage brain study shows.
They do not identify causes. The research shows that rank can shift and abilities can change, but it does not establish which habits, health factors, or experiences drive those changes for a given person.
Old-age samples are not fully representative, since people with lower childhood scores were less likely to survive and take part in follow-ups, which is why the Lothian researchers corrected their estimates.
Frequently Asked Questions
Is IQ fixed after childhood?
Not completely. Rank-order stability is high, with a correlation of .54 between scores at age 11 and age 90 in the Lothian Birth Cohort of 1921, but the 2011 teenage study found that about a third of participants shifted significantly on verbal or nonverbal IQ within four years.
Why is my adult IQ score different from my childhood score?
Several reasons can stack up: real change in your relative ability, measurement error, different tests with different scales, and age norms that compare you with a different reference group. A difference of a few points between two tests years apart is normal and does not by itself mean your ability changed.
Does your IQ drop when you get old?
Your raw speed and novel reasoning tend to decline with age, but your IQ score compares you with people your own age, so it does not drop simply because you are older. A falling age-normed score in later life is a different signal, one worth discussing with a doctor if it comes with everyday memory or thinking problems.
Summary
IQ changes with age in one sense and stays stable in another. Raw abilities shift across a lifetime, with speed and novel reasoning declining from early adulthood while knowledge keeps growing. Your IQ score, measured against people your own age, tends to hold its rank remarkably well from childhood to old age, though not perfectly, and adolescence is a period when real shifts happen. Reading any IQ result with that distinction in mind avoids most of the myths about intelligence and aging.
