What does an IQ of 64 mean for a child?
An IQ of 64 is higher than about 0.82% of people, roughly 1 in 122 scoring at or below it. For an adult it is a fairly settled result. For a young child it is a snapshot: scores before about age 7 change a lot between tests, so one low result is a starting point for support, not a forecast.
How far below average is 64?
An IQ of 64 is 36 points below the average of 100, or 2.4 standard deviations. About 0.82% of people of the same age score lower, the shaded sliver at the far left of the curve below.
On a test with a standard deviation of 16, such as older Stanford-Binet editions, the same result would be about 62, and on the Cattell scale, which uses 24, about 42. Why scales differ.
What an IQ of 64 tells you
A 2024 review of 205 longitudinal studies found that cognitive test scores in young children shift considerably over time. Stability good enough to make decisions about an individual child can only be expected from about age 7, and then only over short periods; from about age 14, scores stay reasonably stable for the rest of life.
That is why psychologists usually re-assess young children and look at development, play, language and daily skills alongside any number. If a young child scores 64, the useful question is what help with speech, learning or everyday routines would make the biggest difference now, not what the score will be in ten years.
How an IQ of 64 is classified
Different tests and manuals use different words for the same score, and the words have changed over time. Here is where 64 falls on each of the systems you are most likely to meet.
Sources: American Psychiatric Association, DSM-5 fact sheet on intellectual disability; World Health Organization, ICD-11, 6A00 disorders of intellectual development; Peltopuro, M. and others (2014), "Borderline intellectual functioning: a systematic literature review", Intellectual and Developmental Disabilities, 52(6), 419–443. WISC-V descriptors from Pearson's interpretive reports, as on our good IQ score guide.
Does 64 mean an intellectual disability?
A score of 64 on its own never makes a diagnosis. The American Psychiatric Association's DSM-5 describes intellectual disability as "approximately two standard deviations or more below the population, which equals an IQ score of about 70 or below", and requires three things together:
- Low intellectual functioning, confirmed by a clinical assessment and individually given, standardised testing.
- Difficulties with everyday adaptive skills in at least one of three domains: conceptual (language, reading, maths, memory), social (communication, judgement, friendships) and practical (personal care, money, work and school tasks).
- A start during the developmental period, in childhood or adolescence.
Severity is set by those everyday skills, not by the IQ number. That is why only about 1% of people have an intellectual disability (a 2011 meta-analysis of 52 population studies found about 10 per 1,000), even though about 2.3% score below 70 on the bell curve. Because tests have a margin of error, DSM-5 treats roughly 65 to 75 as the uncertain zone around 70.
Sources: American Psychiatric Association, DSM-5 fact sheet on intellectual disability; Maulik, P. K. and others (2011), "Prevalence of intellectual disability: a meta-analysis of population-based studies", Research in Developmental Disabilities, 32(2), 419–436; Hall v. Florida, 572 U.S. 701 (2014), which cites the DSM-5 range of 65 to 75.
Is your 64 accurate?
Low scores are the most fragile results on any test, because almost everything that goes wrong on the day pulls a score down. Common reasons include:
- Running out of time. On timed tests, including ours, an unanswered question counts as wrong.
- Nerves. A review of 238 studies found test anxiety consistently linked with lower scores.
- Tiredness. Sleep loss hits attention and speed hardest, which costs points against the clock.
- Language and format. Taking a test in a second language, on a small screen or in an unfamiliar format can lower a result without saying anything about reasoning.
What a 64 means on our test
The Assessivo test moves in steps of about 2.5 points, so it can't give exactly 64: the nearest results are 63 (3 correct) and 65 (4 correct). Every question has four options, so someone guessing every answer at random averages nine correct, a score of 78. Random guessing scores this low only about once in 91 attempts. The likeliest explanations are the clock, a refresh at the wrong moment or a very interesting phone, not your reasoning.
If any of this sounds like your session, retake the free IQ test when you are rested and have 25 quiet minutes. A score that moves a lot between attempts was never very solid.
Sources: von der Embse, N. and others (2018), "Test anxiety effects, predictors, and correlates: a 30-year meta-analytic review", Journal of Affective Disorders, 227, 483–493; Lim, J. and Dinges, D. F. (2010), "A meta-analysis of the impact of short-term sleep deprivation on cognitive variables", Psychological Bulletin, 136(3), 375–389. Guessing figures are worked out from the binomial distribution for 36 four-option questions.
What is the mental age for an IQ of 64?
The first IQ tests, for children, described performance as a "mental age": the age whose typical performance a child matched. IQ was mental age divided by real age, times 100. Run that old formula backwards and you get the figures below, for children only.
| Child's age | Performs like a typical child of about |
|---|---|
| 6 | 3 years 10 months |
| 8 | 5 years 1 month |
| 10 | 6 years 5 months |
| 12 | 7 years 8 months |
| 14 | 9 years |
For adults the idea doesn't work, which is why David Wechsler replaced it in 1939 with today's method: compare each person with others of the same age. An adult who scores 64 has an adult's knowledge, interests and experience. The score only says how their test performance compares with other adults'.
How common is an IQ of 64?
Line up 100 people of the same age and about 1 would score 64 or lower; the orange dot marks the place. In a city of a million, about 8,200 people would be at or below this level.
The bar shows the likely range on a professional test, about five points either way: 59 to 69, from the 0.31th to the 2nd percentile.
How 64 compares with nearby scores
| IQ | Percentile | Classic label | Score this low or lower |
|---|---|---|---|
| 54 | 0.11th | Extremely low | 1 in 924 |
| 59 | 0.31th | Extremely low | 1 in 319 |
| 64 | 0.82th | Extremely low | 1 in 122 |
| 69 | 2nd | Extremely low | 1 in 52 |
| 74 | 4th | Borderline | 1 in 24 |
Questions about an IQ of 64
What percentile is an IQ of 64?
An IQ of 64 is at about the 0.82th percentile: it is higher than about 0.82% of people of the same age, and roughly 1 person in 122 scores this low or lower.
Is 64 a low IQ?
Yes. 64 is 36 points, or 2.4 standard deviations, below the average of 100. On the classic Wechsler labels it is extremely low. A single score is an estimate with a margin of error of about five points, so 64 is best read as roughly 59 to 69.
Does an IQ of 64 mean intellectual disability?
Not on its own. 64 is in the range where an intellectual disability (called a learning disability in the UK) is considered, but a diagnosis also needs significant difficulties with everyday skills that began during childhood, assessed by a qualified psychologist.
What is the mental age for an IQ of 64?
Mental age is an idea from the earliest tests for children. By the old formula, a 10-year-old scoring 64 would perform like a typical child of about 6 years 5 months. For adults it has no meaning: modern IQ tests compare adults with other adults, and an adult who scores 64 is not like a child.
Can a child's IQ of 64 change?
It can, especially in early childhood. A 2024 review of 205 studies found that scores in young children change a lot, with stability good enough for individual decisions only from about age 7. Re-assessment, and support matched to the child's needs, are standard practice.
Related: the IQ range chart, what counts as an average IQ, what IQ measures and misses and how to tell if an online IQ test is accurate.
Behind a single score of 64 sit several separate abilities. Read about processing speed, fluid vs crystallized intelligence, abstract reasoning, spatial reasoning and verbal reasoning, or try the free pattern recognition test.
Information and support
If a professional assessment has given you, your child or someone you care for a score like 64, these organisations explain what it means in practice and what help is available.
Want a second reading?
Take the free Assessivo IQ test when you are rested and have 25 quiet minutes: 36 questions, and your estimated score and percentile as soon as you finish.
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