How is an IQ score calculated on modern intelligence tests?

Modern intelligence tests, such as the Stanford-Binet Intelligence Scale and the Wechsler scales, calculate IQ scores based on statistical distributions rather than the original ratio of mental age to chronological age.1234

The IQ score represents an individual's standing relative to a normative group. This means a score indicates how a person performed compared to others of a similar age or background. Most intelligence tests yield an overall IQ score, while some, like the Wechsler scales, also provide separate scores for verbal and performance subtests.31

Intelligence test scores typically follow a normal distribution, with most scores clustering around the average of 100. Approximately two-thirds of scores fall between 85 and 115, and about 95% fall between 70 and 130.45