Know your BMI

Select your height  


Introduce your weight

What your BMI means

BMI is a calculation of your size that takes into account your height and weight.

What’s a normal BMI?

A normal BMI is between18.5 and 25; a person with a BMI between 25 and 30 is considered overweight; and a person with a BMI over 30 is considered obese. A person is considered underweight if the BMI is less than 18.5.

As with most measures of health, BMI is not a perfect test. For example, results can be thrown off by pregnancy or high muscle mass, and it may not be a good measure of health for children or the elderly.

So then, why does BMI matter?

In general, the higher your BMI, the higher the risk of developing a range of conditions linked with excess weight, including:

  • diabetes
  • arthritis
  • liver disease
  • several types of cancer (such as those of the breast, colon, and prostate)
  • high blood pressure (hypertension)
  • high cholesterol
  • sleep apnea.

Current estimates suggest that up to 365,000 excess deaths due to obesity occur each year in the U.S. In addition, independent of any particular disease, people with high BMIs often report feeling better, both physically and psychologically, once they lose excess weight.

And here’s why BMI may not matter

It’s important to recognize that BMI itself is not measuring “health” or a physiological state (such as resting blood pressure) that indicates the presence (or absence) of disease. It is simply a measure of your size. Plenty of people have a high or low BMI and are healthy and, conversely, plenty of folks with a normal BMI are unhealthy. In fact, a person with a normal BMI who smokes and has a strong family history of cardiovascular disease may have a higher riskof early cardiovascular death than someone who has a high BMI but is a physically fit non-smoker.

Bottom line

As a single measure, BMI is clearly not a perfect measure of health. But it’s still a useful starting point for important conditions that become more likely when a person is overweight or obese. In my view, it’s a good idea to know your BMI. But it’s also important to recognize its limitations.