A BMI between 18.5 and 24.9 is healthy for men and women over the age of 18, according to the Centers for Disease Control. The National Heart, Lung and Blood institute offers an online BMI calculator and BMI tables for adults. Individuals under 18 should consult a different chart.
The CDC offers an online BMI calculator for individuals 2 to 19 years old that compensates for age, height and gender.
A body mass index is a generalized measurement applicable to most adult men and women, and not a specific measurement of health, explains the National Heart, Lung, and Blood Institute. While considered to be a useful tool in determining general health, it can overestimate body fat percentages in athletes and underestimate body fat percentages in the elderly. The National Institutes of Health recommend using waist measurements in addition to BMI in order to determine health.