Your BMI can tell you if you're carrying too much weight, but it cannot tell if you're carrying too much fat.

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The BMI cannot tell the difference between excess fat, muscle or bone.

The adult BMI does not take into account age, gender or muscle mass.

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This means:

• very muscular adults and athletes may be classed "overweight" or "obese" even though their body fat is low

• adults who lose muscle as they get older may fall into the "healthy weight" range even though they may be carrying excess fat

 

Pregnancy will also affect a woman's BMI result. Your BMI will go up as your weight increases. You should use your pre-pregnancy weight when calculating your BMI.

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Apart from these limitations, the BMI is a relatively straightforward and convenient way of assessing someone's weight.

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- NHS UK