How IQ Is Estimated for Presidents Without Test Scores
No U.S. president has taken a published IQ test. Here is the method behind the numbers—and what it cannot do.
The achievement-age method
Catharine Cox (1926) compiled chronologies of childhood and young-adult achievements for 301 eminent historical figures. For each achievement, she identified the age at which it appeared and compared that to the age at which the same achievement would be expected in the general population. IQ was then calculated as 100 times mental age divided by chronological age. A person who does at 20 what most people do at 25 gets a higher estimate. The method is historiometric: it infers intelligence from biographical records rather than from a administered test.
Why there are four estimates per president
Cox split each person's life into two windows: Period I (birth to age 17) and Period II (ages 18 to 26). She also applied a correction for attenuation—a statistical adjustment upward to compensate for thin or unreliable biographical data. Crossing these two choices produces four variants: I-U, I-C, II-U, and II-C. The II-C variant (ages 18-26, corrected) is consistently the highest, because the 18-26 window captures more cognitive signal and the correction compensates for missing data. Across the eight presidents Cox originally rated, the correction adds about 14 IQ points on average, and the 18-26 window scores about 11 points higher than the 0-17 window.
| Variant | Age range | Corrected? | What it means |
|---|---|---|---|
| I-U | 0-17 | No | Raw childhood estimate; most conservative |
| I-C | 0-17 | Yes | Childhood adjusted for thin biographical data |
| II-U | 18-26 | No | Raw young-adult estimate |
| II-C | 18-26 | Yes | Strongest single estimate; the one this atlas displays |
What the full method requires
Simonton's 2006 study did not stop at Cox's IQ estimates. He combined them with two additional measures using expectation-maximization (EM) imputation: Intellectual Brilliance (independent judges rated anonymous biographical profiles on 300 adjectives) and Openness to Experience (presidential experts rated each president on the NEO personality inventory). The three measures are highly correlated—around 0.70—so any one can help predict the others. The EM algorithm used all available data to fill in missing values across all 42 presidents. A rigorous extension to new presidents would require all three: a Cox-style achievement chronology, expert personality ratings, and the EM imputation pipeline.
What is missing for modern presidents
Obama, Trump, and Biden are outside Simonton's 2006 study. Extending the full method to them faces four obstacles. First, no modernized achievement-age scale exists; Cox's 1926 scale reflects 19th-century educational norms. Second, no published NEO Openness or Intellectual Brilliance ratings exist for these presidents. Third, Cox used three independent raters with psychometric expertise; a single-rater assessment would be far less reliable. Fourth, the correction-for-attenuation factor was calibrated on thin historical biographies, not on modern figures with abundant documentation.
Our qualitative adaptation
Rather than abandon the method entirely, we apply its logic qualitatively. We compile a year-by-year chronology of each president's intellectual achievements from ages 18 to 26 using public biographical sources (Wikipedia, news archives, presidential libraries). We compare each achievement to when it would be expected in the general population. We then place each president in the Simonton II-C distribution (which ranges from 130 to 175, with a mean of 147) based on the strength of the evidence. The result is an informal estimate—not a validated historiometric score. It is more rigorous than a guess, but it lacks the expert ratings, multiple raters, and EM imputation that make Simonton's values defensible. Each president's detailed chronology and assessment is available on its own page.