IQ Percentile Calculator

How IQ Percentile Calculator Works

IQ scores are designed to follow a normal distribution with a mean of 100 and a standard deviation of 15 — the calculator converts your score into a z-score (how many standard deviations from average it is) and then applies the standard normal distribution to find what percentage of people would be expected to score at or below that value.

Who Uses IQ Percentile Calculator and Why

• Converting a raw IQ test score into a percentile to understand roughly what proportion of people would be expected to score lower.
• Comparing scores from tests with different scaling (like an older test using SD 16 rather than 15) after checking which standard deviation applies, per the calculator's own FAQ.
• Explaining what an IQ score "means" in relative terms to someone unfamiliar with standard deviations or z-scores.
• Cross-checking a percentile figure quoted in an article or report against the standard normal distribution math it should be based on.

Mistakes to Avoid

• Assuming every IQ test uses the same scale — the calculator's FAQ notes most modern tests use mean 100 / SD 15, but some older or specialized tests use a different standard deviation, and using this calculator's assumptions on a test with a different scale gives a wrong percentile.
• Treating the percentile output as a precise, error-free measurement of intelligence — IQ tests themselves carry measurement error and test-retest variability, which a percentile conversion doesn't remove.
• Confusing percentile with score — a percentile of 90 doesn't mean "90 IQ points," it means scoring higher than about 90% of the reference population.

Tips for Best Results

• Check what standard deviation your specific test uses before relying on the percentile result, since the calculator assumes the common 100/15 scale by default.
• Remember the normal distribution is a designed property of test scoring calibration, per the FAQ, not an independently verified fact about the general population — treat percentile results as a scoring convention, not an absolute truth about intelligence distribution.

Fixing Common Problems

The percentile seems too extreme for my score (like 99.9th percentile for a moderately high IQ). — Very high or low IQ scores sit many standard deviations from the mean, where the normal distribution's tail produces percentiles that climb steeply — double-check your test's actual standard deviation matches the 15-point default this calculator assumes.

Terms Explained

Z-score: A measure of how many standard deviations a value is from the mean — the intermediate step used to convert a raw IQ score into a percentile.

Standard normal distribution: The bell-curve probability distribution (mean 0, standard deviation 1) used to translate a z-score into the percentage of people expected to score at or below a given value.