— Guide
What is the average IQ?
The average IQ is 100, by definition. This is not an empirical finding — it's how the scale is constructed. IQ tests are standardised so that the population mean is always 100, with a standard deviation of 15. Whenever a test is re-normed (which happens every decade or so), the new midpoint is anchored back to 100.
Roughly two-thirds of the population (68%) score between 85 and 115 — the conventional "normal range". Another 27% scores between 70–85 or 115–130. Only about 5% falls outside the 70–130 window in either direction.
Why exactly 100?
The number is a historical convention. When Alfred Binet developed the first widely-used intelligence test in 1905, scores were expressed as a "mental age" ratio — your performance compared to the typical performance for your chronological age, times 100. A child performing at exactly their age level scored 100. The convention stuck even after the ratio model was abandoned for modern norm-referenced scoring.
Today's tests no longer compute a ratio. Instead, your raw performance is mapped onto the standard normal curve and rescaled so the mean is 100 and SD is 15. The number 100 is preserved purely because it's familiar and avoids re-explaining the scale every few decades.
Is the average rising? (The Flynn effect)
Raw cognitive performance — the number of items answered correctly on a fixed test — has risen substantially across the 20th century. James Flynn documented gains of roughly 3 IQ points per decade across most developed countries between 1930 and 2000. This is known as the Flynn effect.
The Flynn effect doesn't mean the "average IQ" is rising past 100, because tests are re-normed to keep the mean anchored. It means that today's 100-point performance corresponds to noticeably more raw items correct than the 100-point performance of 50 years ago.
Several large studies since 2000 (Norway, Denmark, UK, France) have found the Flynn effect has stalled or reversed — small but consistent declines on standardised reasoning tests. The cause is still actively debated.
Does average IQ differ by country?
Cross-national IQ comparisons are technically possible but methodologically very fraught — sampling differences, translation effects, education differences, and cultural familiarity with test formats all confound the comparison. Published cross-country estimates have wide error bars and should be read with significant skepticism.
Within any given country, IQ varies substantially across individuals — far more than the average varies across countries. The 5th-95th percentile spread within one population (roughly 75–125) easily exceeds the largest claimed cross-country gaps.
What's a "normal" IQ?
The standard clinical convention:
- 70–85 — Below Average (16% of population)
- 85–115 — Average / Normal Range (68% of population)
- 115–130 — Above Average (14% of population)
- 130+ — Gifted (2.3% of population)
"Average" is genuinely a wide band. A 95 and a 110 are statistically very close together — both clearly within the normal range, and well within typical test-retest variation.
Take a calibrated test
Core Brain runs a 3PL Bayesian IRT estimator with items calibrated to the standard normal distribution. Twenty minutes, six cognitive axes, a normed IQ score with a 95% confidence interval — so you can see exactly where you sit relative to the 100-point average.
Take the Core Brain IQ test →