IQ 55
What does an IQ of 55 mean?
55 is near three standard deviations below the mean. Here is what the number means on the scale, and why a short online test can never be the last word on a score this low.
Short answer
An IQ of 55 is well below average. It is higher than about 0.13% of people, which puts it at the 0.13 percentile. About 1 in 740 people score 55 or lower, and the WAIS-IV labels it Extremely Low (69 and below). It is 3 standard deviations below the mean of 100.
Specimen · IQ 55
55IQ
- Classification
- Extremely Low
- Percentile
- 0.13
- Rarity
- 1 in 740
- z-score
- −3.00
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| Percentile | 0.13 |
| Share scoring 55 or lower | 0.13% (about 1 in 740) |
| Out of 1,000 people | about 1 at or below |
| Standard deviations from the mean (z) | -3.00 |
| WAIS-IV classification | Extremely Low (69 and below) |
| Same percentile, SD 16 scale | 52 |
| Same percentile, SD 24 scale | 28 |
What an IQ of 55 means on the scale
Modern IQ tests report a deviation IQ: scores are standardized so the mean is 100 and the standard deviation is 15 within each age group (Wikipedia: Intelligence quotient). On that scale 55 is 3 standard deviations below the mean. It sits exactly three standard deviations from the mean, at the edge of the 55 to 145 range where about 99.7% of people score. (the 68-95-99.7 rule)
In a room of 30 people your age, fewer than 1 (about 1 in every 741 groups of 30) would be expected to score 55 or lower. Put another way, about 100 out of every 100 people score above 55.
The Extremely Low band: 69 and below
Extremely Low is the WAIS-IV label for scores of 69 and below, more than two standard deviations under the mean (Wikipedia: IQ classification). From the normal curve, about 2.1% of people score in this range. Scores near 55 are close to three standard deviations below the mean, the edge of the range that holds about 99.7% of people.
A score this low from a short online test should be treated as unreliable. Misreading the instructions, skipping items, running out of time or testing on a phone can all produce it. If you have real questions about a learning or intellectual disability, for yourself or someone you care for, a licensed psychologist can give a full standardized assessment.
Where 55 sits inside the band
55 is 14 points below the top of the Extremely Low band (69). Of the people who score in this band, about 5.8% score below 55, so it is near the bottom of the group that shares its label.
Clinical IQ scores carry measurement error of around plus or minus 5 points at 95% (Wechsler, 2008). A measured 55 is consistent with a true score anywhere from 50 to 60, which is the 0.04 to 0.38 percentile. That whole range stays inside the Extremely Low band, so the label is the most stable part of the result. A short online test has a wider range than a clinical one, so read any single number as the middle of a span.
What an IQ of 55 does and does not predict
Only a full clinical assessment, not one number from one session, can say what a score in this range means for a particular person.
Across large groups, the links are real. General intelligence at age 11 correlated 0.81 with exam results at 16 in about 70,000 English children (Deary, Strand, Smith & Fernandes, 2007), a review of 85 years of workplace research put the link with job performance at 0.51 (Schmidt & Hunter, 1998), and a 2007 meta-analysis found correlations of about 0.56 with education and 0.23 with income (Strenze, 2007). Those describe tendencies across many people. None of them let anyone predict an individual life from one number. The guide to what IQ predicts explains what a correlation of that size means.
Same score, different tests
Older Stanford-Binet forms used a standard deviation of 16, and the Cattell Culture Fair III scale uses 24 (Wikipedia: IQ classification). The same percentile as 55 on a standard-deviation-15 test reads as about 52 on the first and 28 on the second, so check which scale a number is on before comparing scores from different tests.
Nearby scores
| IQ | Percentile | Rarity | Classification |
|---|---|---|---|
| IQ 56 | 0.17 | 1 in 600 | Extremely Low |
| IQ 57 | 0.21 | 1 in 480 | Extremely Low |
| IQ 58 | 0.26 | 1 in 390 | Extremely Low |
| IQ 70 | 2.3 | 1 in 44 | Borderline |
IQ 56 · every score on the IQ chart · IQ percentile calculator · the seven classification bands
Sources
- Intelligence quotient. Wikipedia. en.wikipedia.org/wiki/Intelligence_quotient
- IQ classification. Wikipedia. en.wikipedia.org/wiki/IQ_classification
- 68-95-99.7 rule. Wikipedia. en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule
- Wechsler, D. (2008). WAIS-IV Technical and Interpretive Manual. Pearson.
- Deary, I. J., Strand, S., Smith, P., & Fernandes, C. (2007). Intelligence, 35(1), 13-21. doi.org/10.1016/j.intell.2006.02.001
- Schmidt, F. L., & Hunter, J. E. (1998). Psychological Bulletin, 124(2), 262-274. doi.org/10.1037/0033-2909.124.2.262
- Strenze, T. (2007). Intelligence, 35(5), 401-426. doi.org/10.1016/j.intell.2006.09.004