There is no difference in the BMI formula: weight (lb) / [height (in)]2 x 703, which is used for men, women and children, notes the CDC. Standard weight categories are applied to any adults over 20 years of age, but for children weight categories are relative to age and sex.
At the same BMI, women often have more fat than men and older people tend to have more fat than younger people, according to the CDC. According to the BMI weight categories, a person with a BMI of 25 is considered overweight and a person with a BMI of 30 is obese. There are exceptions to this rule, such as athletes. BMI does not measure only fat but also measures a person's weight, which includes fat and muscle.