Is an IQ of 59 an intellectual disability?
Not by itself. An IQ of 59 is very low, higher than only about 0.31% of people, and it is in the range where psychologists consider an intellectual disability. But a diagnosis also needs real difficulties with everyday life that began in childhood, which is why far fewer people have an intellectual disability than score below 70.
59 on the IQ bell curve
An IQ of 59 is 41 points below the average of 100, or 2.73 standard deviations. About 0.31% 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 56, and on the Cattell scale, which uses 24, about 34. Why scales differ.
Reading an IQ of 59
On a perfect bell curve, about 2.3% of people score below 70. Yet when researchers pooled 52 population studies, the prevalence of intellectual disability came out at about 10 per 1,000 people, roughly 1%. The gap exists because a low score is only one of the three things a diagnosis requires.
The other two are difficulties with everyday adaptive skills, and a start during the developmental period, in childhood or adolescence. Someone who scores 59 on one test but manages school, work and daily life independently would not usually be diagnosed, and a psychologist would look carefully at whether the test result itself was accurate.
How an IQ of 59 is classified
Different tests and manuals use different words for the same score, and the words have changed over time. Here is where 59 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.
When is 59 part of an intellectual disability?
A score of 59 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.
Before you trust a 59
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 59 means on our test
The Assessivo test moves in steps of about 2.5 points, so it can't give exactly 59: the nearest results are 58 (1 correct) and 60 (2 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 2,420 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 59?
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 6 months |
| 8 | 4 years 9 months |
| 10 | 5 years 11 months |
| 12 | 7 years 1 month |
| 14 | 8 years 3 months |
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 59 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 59?
Line up 100 people of the same age and about 1 would score 59 or lower; the orange dot marks the place. In a school of 1,000 pupils, you would expect about 3 at or below this level.
The bar shows the likely range on a professional test, about five points either way: 54 to 64, from the 0.11th to the 0.82th percentile.
How 59 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 |
Questions about an IQ of 59
What percentile is an IQ of 59?
An IQ of 59 is at about the 0.31th percentile: it is higher than about 0.31% of people of the same age, and roughly 1 person in 319 scores this low or lower.
Is 59 a low IQ?
Yes. 59 is 41 points, or 2.73 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 59 is best read as roughly 54 to 64.
Is 59 IQ an intellectual disability?
Not on its own. 59 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 59?
Mental age is an idea from the earliest tests for children. By the old formula, a 10-year-old scoring 59 would perform like a typical child of about 5 years 11 months. For adults it has no meaning: modern IQ tests compare adults with other adults, and an adult who scores 59 is not like a child.
What percentage of people have an intellectual disability?
About 1%. A 2011 meta-analysis of 52 population-based studies put the prevalence at about 10.4 per 1,000 people. That is less than the 2.3% who score below 70 on the bell curve, because a diagnosis also needs difficulties in everyday functioning that start in childhood.
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.
An IQ test arrives at a score like 59 by combining several kinds of task. Learn more 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 59, 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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