Average IQ for adults, by age

An IQ is not a raw score. When a test is built, the publisher gives it to a large sample of people of each age. Your raw score is then compared only with people your own age, and converted to a scale where the middle of that age group is 100 and the standard deviation is 15.

That is why a 10-year-old and an 18-year-old can both have an IQ of 100 while solving very different problems. The number tells you where someone stands among their peers, not how much they know. It also means that there is no such thing as an average IQ that rises with age.

Adult IQ scores reflect the interplay between fluid intelligence (which peaks in the mid-20s and gradually declines) and crystallized intelligence (which continues to grow through middle age). The average adult IQ is 100 by definition. Most cognitive abilities remain stable through the 60s, with only processing speed showing significant age-related decline before age 65.

• Fluid intelligence peaks between ages 20-25 and gradually declines at approximately 1-2 points per decade
• Crystallized intelligence (vocabulary, general knowledge) continues to increase until ages 60-70
• Overall IQ remains relatively stable from 25-65 as crystallized gains offset fluid losses
• Processing speed shows the earliest and most significant age-related decline, beginning in the late 20s
• Working memory capacity peaks in the early 20s and declines modestly through middle age
• Education, occupational complexity, and continued learning can buffer age-related cognitive decline
• Physical exercise, particularly aerobic exercise, is associated with preserved cognitive function in middle age

Adulthood illustrates the classic divergence between fluid and crystallized intelligence. Fluid intelligence (novel problem-solving, abstract reasoning) peaks in the mid-20s, then declines gradually. Crystallized intelligence (accumulated knowledge, vocabulary, expertise) continues growing well into the 60s. This is why experienced professionals often outperform younger colleagues despite slower processing speed.

How people this age are tested

The WAIS-IV is the standard adult intelligence test. Online IQ tests can provide rough estimates but lack clinical standardization. Factors affecting adult IQ scores include: sleep quality, stress levels, medication, alcohol consumption, and testing conditions. A comprehensive assessment takes 60-90 minutes and should be administered by a licensed psychologist.

The average above is a statistic, not a test. The IQ test for adults page explains how the LifeScore test works for this group: the same 25 puzzles for everyone, not age-normed, and honest about what the number can show. Pick the page that matches the age you have in mind.

Two tools go with this page. The average IQ by age calculator turns a score into a percentile for an age group. The mental age calculator shows the old ratio formula, which only made sense for children.