Most IQ scores fall within 15 points of a median score of 100. A normal distribution of IQ scores around this median means that 86 percent of scores fall within one standard deviation, or between 85 and 115. All but 5 percent fall within two standard deviations.

IQ tests are calibrated in order to establish a median score of 100, which is usually regarded as average. The further a score deviates from the median, the fewer people achieve it. Only a small fraction of test takers score higher than 130 or lower than 70, which are usually considered the bounds of normal IQs.