Top 0.5%
What IQ is the top 0.5 percent?
A cut this far out is rarer than one person in a hundred. Here is the score on three common scales, and why numbers this high are hard to measure.
Short answer
The top 0.5% of IQ scores starts at about 139 on the standard scale (mean 100, standard deviation 15); the exact cut is 138.6. That is the 99.5th percentile, about 1 in 200 people. On a scale with standard deviation 16 the cut is about 141, and on the SD 24 Cattell scale about 162.
Specimen · Top 0.5%
0.5%Top
- Cut at
- IQ 138.6
- Classification
- Very Superior
- z-score
- +2.58
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| Scale | IQ at the 99.5th percentile |
|---|---|
| Standard deviation 15 (Wechsler, SB5) | 138.6 |
| Standard deviation 16 (older Stanford-Binet) | 141.2 |
| Standard deviation 24 (Cattell Culture Fair III) | 161.8 |
How the cut is calculated
IQ scores are standardized to a normal curve with mean 100 (Wikipedia: Intelligence quotient). To find the score at a percentile, take the z score that leaves 0.5% of the curve above it, multiply by the scale's standard deviation and add 100. For the 99.5th percentile the z score is 2.576, so the cut is 138.6 on SD 15. Older Stanford-Binet forms used SD 16 and the Cattell Culture Fair III scale uses SD 24 (Wikipedia: IQ classification), which is why the same percentile reads as 141.2 and 161.8 there. The percentile to IQ converter does this for any percentile.
Scores this rare are hard to measure
The top 0.5% is about 5 people in every 1,000. A test needs enough hard items to separate people this far out, and every test has a ceiling where it runs out of them. Clinical scores also carry measurement error of around plus or minus 5 points at 95% (Wechsler, 2008), which matters more here than anywhere else: a measured 139 is consistent with a true score from 134 (about the 98.8 percentile) to 144.
That is why careful reports at this level give a range, not a bare number, and why a claim of an exact score far above 145 should always come with the test, the scale and the confidence range.
A percentile is not a percentage of questions
The 99.5th percentile means scoring higher than 99.5% of people the same age, not answering that share of questions correctly. See whether an IQ score is a percentage for the difference.
Neighboring percentiles
| Percentile | IQ (SD 15) | Gap from 139 |
|---|---|---|
| Top 0.1% | 146.4 | +7.7 |
| Top 1% | 134.9 | -3.7 |
See the score itself on IQ 139, every cut on the IQ by percentile page, or any score on the IQ score chart.
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.