Why Standard Tests Cap Out Around 160
Modern IQ tests are standardized using large population samples. The questions are calibrated so that the full range of difficulty in the test covers the range of ability from about 55 to 160. At IQ 160, an individual answers essentially every question correctly — there are no harder questions left to distinguish them from someone at IQ 165 or 175.
To measure above 160, researchers must either use specialized extended-range tests (like those developed for high-IQ societies) or extrapolate from the pattern of performance — calculating what score would be implied by the speed, age, and completeness of correct answers.
The Ratio IQ Method and Child Prodigies
The scores above 200 that appear in popular accounts almost always come from one of two sources: the old Stanford-Binet ratio method applied to young children, or retrospective biographical estimation.
The ratio method calculates IQ as (Mental Age / Chronological Age) × 100. A 10-year-old performing at the mental level of a 22-year-old yields a ratio IQ of 220. This is how Marilyn vos Savant's score of 228 was obtained — she was 10, performing at the level of a 22-year-old.
The problem is that this formula produces larger scores the younger the test-taker is. The same level of adult performance, tested at age 10, yields a much higher number than tested at age 20. This is why childhood IQ records don't reflect real-world adult differences in cognitive ability.
Who Claims IQ Over 200?
William James Sidis (250–300 estimated)
The highest estimate on record. Sidis never took a formal IQ test, so his estimate is purely biographical — calculated by psychologist Abraham Sperling based on his documented abilities. He entered Harvard at 11, spoke 40+ languages, and produced original mathematical and philosophical works. The 250–300 range is extrapolated from performance, not measured. Read the full story in our Sidis IQ article.
Marilyn vos Savant (228)
Her score is the most "official" of the group, as it was obtained by a trained psychologist using the Stanford-Binet scale. However, as explained above, the ratio method applied to a 10-year-old inflates the number significantly compared to what a deviation IQ scale would yield for the same ability level in an adult.
Terence Tao (225–230)
Tao's scores are the most credible high-range results. He was formally tested using extended-range procedures as part of Julian Stanley's Study of Mathematically Precocious Youth (SMPY) at Johns Hopkins. The 225–230 range reflects genuine measured performance on appropriately difficult items.
What Does Life Look Like at IQ 200+?
Those who have been studied in this range describe a qualitatively different experience of thinking. Concepts that others find difficult appear obvious. Complex systems are grasped as wholes rather than as collections of parts. Mathematical structures have an almost sensory immediacy. Language and abstract reasoning feel effortless in the domains of their interest.
But this extraordinary cognitive ability does not translate automatically into extraordinary life outcomes. Sidis died in obscurity. Many high-IQ individuals report social isolation and difficulty connecting with people who think differently. The correlation between IQ and happiness is real but modest — far weaker than the correlation between IQ and academic achievement. Visit IQ 200 profiles for more.