What is the formula for calculating IQ?

The formula for calculating IQ that is widely accepted and historically significant is based on the ratio of mental age to chronological age, multiplied by 100. This method was first developed by psychologist Lewis Terman in the early 20th century.

In this formula, mental age refers to the age at which an individual performs on standardized tests (i.e., the level of intellectual functioning), while chronological age is the actual physical age of the individual. By dividing mental age by chronological age, you get a ratio that reflects how a person's cognitive abilities compare to their peers. Multiplying this ratio by 100 allows for a standardized score that can be interpreted more easily.

Thus, the correct formula effectively provides a quantified measure of intelligence, allowing for comparisons across different age groups. This method was particularly useful when IQ testing was first being established, as it helped identify students who might require additional educational support based on their cognitive abilities relative to their age group.