Is the BMI Calculator Really Accurate?

Since the 1980’s, the Body Mass Index (BMI) chart has been used internationally to determine obesity. The American public learned about the standard in the 1990’s, and with the presence of online tools today it’s possible to calculate your BMI in just seconds.

The BMI formula takes into account weight and height to help you figure out which category of the chart you’re in. There are four categories: obese, overweight, normal weight, and underweight.

Because a person’s healthy weight is largely affected by how tall or short he or she is, the BMI calculator is a handy way to get an idea of what an appropriate weight is. If you’re nearly six-feet tall, for instance, you may weigh quite a bit more than an average five-foot-tall person and yet still be underweight.

BMI Calculator Accuracy

But while the BMI chart is a simply and quick way to see what an average healthy weight for a person of your height is, it does have multiple drawbacks and shortcomings and isn’t always an accurate gauge of how healthy or unhealthy you are.

One of those shortcomings is the fact that the Body Mass Index can’t factor in the location of your body fat. Belly fat, or fat which surrounds your internal organs, is far more dangerous and indicative of a greater chance for diabetes, heart-related illnesses, and even early death. But body fat stored elsewhere in the body may not pose much of a health risk at all.

Furthermore, physicians have also realized that having some extra body fat is actually beneficial at times. Some people with chronic illnesses may benefit from the extra energy stored in fat. And although overweight people are more at risk for diseases such as type two diabetes, they often seem to be able to handle the condition better than those who are thin and affected with the same condition.

Besides that, research has shown that 8% of those who fall into the “normal weight” category are metabolically unhealthy despite the fact that they are considered to be slender. But because they aren’t overweight or obese, their metabolic unhealthiness is not detected or suspected.

Look at this chart from a recent study. Study purpose was: To determine the effect of metabolic status on all-cause mortality and cardiovascular events in normal-weight, overweight, and obese persons.


  • Athletes and other people who work out regularly pose another problem for the BMI system, since they may have more muscle than average. Because muscle weighs a lot, someone with a very low percentage of body fat may be categorized as overweight or even obese. This is common among people such as NFL football players, who commonly have a BMI which would place them in the “obese” section.
  • Elderly people may have the exact opposite problem when it comes to the BMI chart. They may register as being a normal weight, but still have a dangerous amount of body fat. This is because they’ve lost bone and muscle density over the years. This loss results in a lower body weight, which means that a higher amount of body fat isn’t going to be noted by a simple BMI calculation.
  • The Body Mass Index simply doesn’t have the ability to take into consideration a wide range of factors such as genetics, ethnicity, age, or even gender. So why is the system still used on a daily basis by insurance companies, doctors, and public health authorities when the BMI calculator accuracy is so questionable?

bmi-acuraccyThe reason is largely because of the fact that the BMI system is simple, inexpensive, and often correct. The BMI system only needs to know two variables: weight and height to be used, making it quick and easy to calculate. Furthermore, it doesn’t require any fancy tools or equipment — a scale and ruler are all that are needed. And because the numbers for obesity and normal weight are based on international averages, the chart is correct more often than not.

Yet, these very factors are the ones which also make the BMI prone to failure. Because only two variables are considered, many other possible conditions are ignored entirely. And because the numbers are only based on averages of large populations, they fail to take into account the simple fact that each person is an individual with specific issues and conditions.

While other tests for measuring body fat do exist, they generally require an expert, as well as expensive equipment and tests. Therefore, until a system with is both cheap and more accurate in calculating healthy weight is found, it’s likely that the BMI will remain a standard tool. But even as we continue to use it, we would do well to remember that the BMI is limited in its ability to truly measure health.

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