How is IQ typically calculated?

The calculation of IQ, or Intelligence Quotient, traditionally uses the formula that involves taking the mental age and dividing it by the chronological age, then multiplying by 100. This method was originally developed by the French psychologist Alfred Binet in the early 20th century, aiming to identify students who required additional educational support.

The formula reflects the concept that if a child’s mental age matches their chronological age, they have an IQ of 100. For instance, if a child is 10 years old (chronological age) and displays the cognitive abilities of a 10-year-old (mental age), the IQ would be (10/10) × 100 = 100. If their mental age were higher, say 12, the IQ would be (12/10) × 100 = 120, indicating above-average intelligence. Conversely, if the mental age is lower than the chronological age, the IQ would be below 100, suggesting below-average cognitive development.

This approach effectively allows for a standardization of intelligence measurements across different ages, expressing cognitive abilities in a way that can be compared across the population.