What does an IQ of 90 mean?
Below the average on the reference scale, at approximately percentile 25.25.
- IQ score
- 90
- Percentile
- 25.25
- At or above
- 74.75%
Normal reference · mean 100 · SD 15. These are calculated values, not observed starp population ranks.
Where 90 sits on the IQ scale
A score of 90 is 10 points below the mean. Dividing by the standard deviation gives (90 − 100) ÷ 15 = -0.67. The normal cumulative distribution converts that standardized position into percentile 25.25.
This lies in the lower half of the central 85–115 interval. A position below the mean is a comparison with the scale center, not a statement that every reasoning skill is below average.
How common is a score of 90?
Approximately 25.25% of this model lies at or below 90—about 1 in 4. This is a cumulative share, not the chance of scoring exactly 90. A continuous model does not assign a positive probability to one exact value.
Compared with IQ 85, the reference percentile is 9.38 percentage points higher. Equal IQ-point gaps do not create equal percentile gaps: the middle of the bell curve contains more area than its ends.
Compare nearby scores
Compare 85 and 90 or calculate 90 on another scale. A small difference between test results is not automatically a meaningful change.
How this relates to starp
starp's current 30-question scoring map produces 90 from 20 correct answers (66.67% correct). That accuracy percentage is different from the normal-model percentile above. The scoring map was calibrated with 12,700 simulated assessments; it is not population norming.
See the scoring method and how raw scores differ from IQ estimates.
Questions about IQ 90
Is 90 a good IQ score?
90 is below the reference mean of 100. It should be interpreted in the context of the test, rather than as a verdict on a person's abilities or future.
What percentile is an IQ of 90?
On a normal scale with mean 100 and standard deviation 15, 90 corresponds to approximately percentile 25.25. Around 74.75% of that model lies at or above it. Use an assessment's own norms for an actual reported rank.
Does an IQ of 90 mean 90% correct?
No. IQ is a scaled score. Percentage correct depends on the questions and scoring rules; percentile describes a relative position. These three quantities are not interchangeable.
Method: NIST's normal-distribution formula. Percentiles here are calculated reference values, not observed starp population ranks. About starp scoring.