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Step 1
Consider yourself underweight if your body mass index is under 18.5 for adults over 20 years old. Consider yourself at a normal body weight if your body mass index is between 18.5 and 24.9.
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Step 2
View your body as overweight if your body mass index is between 25 and 29.9. View your body as obese if your body mass index is more than 30.
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Step 3
Use the body mass index as an indicator of the level of fat on your body. Understand that women tend to have more body fat than men do, and older people typically have more body fat than younger people.
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Step 4
Consider that the body mass index does not take into account your muscle mass. Athletes that train hard may have a high BMI because of their high level of muscularity, so their BMI is not an indicator of fat but an indicator of their weight-to-height ratio.
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Step 5
Decipher body mass index numbers by understanding that it's a cheap way to look at your level of physical fitness. More expensive ways to determine the level of fat on your body do exist. One of the primary ways is a test during which you submerge your entire body in water.
