Your chronological age, that is, the number of years since the day of your birth, does not always align with what psychologists term your “mental age.” Determining the difference between the two is useful in designing lesson plans for the especially intelligent and mentally disabled, though the methods by which psychologists calculate mental age are limited. Standardized tests like the Stanford-Binet intelligence quotient have proven reliable, while doctor assessments in cases of severe disability are little more than educated guesses. Still, doctor assessments demonstrated reliability equal to that of testing in a 1986 study published in the "Journal of Pediatric Psychology."

### Step 1

Take an IQ test administered by a qualified, professional proctor. Online tests can be fun, but they lack expert analysis and come with warnings that they are for entertainment purposes only.

### Step 2

Write down your score in the following formula: IQ=MA/CA * 100, where “MA” is your mental age and “CA” is your chronological age. For example, if your chronological age is 10 and your IQ score is 120, the formula would read, 120=x/10 * 100, where “x” is your mental age.

### Step 3

Divide both sides of the equation by 100. This leaves you with 1.2=x/10 because dividing the right side of the equation cancels out the multiplier of 100, and dividing the left side of the equation, or 120/100, equals 1.2.

### Step 4

Multiply both sides of the equation by 10 to solve for "x," or your mental age. Since "x" is currently the numerator in the fraction x/10, multiplying by 10, or 10/1 to be specific, yields 10x/10, or simply, "x." Multiplying the left side of the equation equals 12, or 1.2 * 10. Therefore, x=12. So in this example, your mental age is 12.

### Warning

Cognitive development slows at 16, then stops at 18, making the calculation of mental age irrelevant. IQ tests for adults use a "standard deviation" formula measured against a mean score of 100. No mental age calculation is used in the IQ scores of adults.