The BMI can be wrong

BMI: What you need to know about the BMI calculator

Is Your Weight Healthy? This question is not always easy to answer. The BMI is supposed to help with the classification and gives a better feeling for where the normal weight of a person lies. This makes it easy to calculate whether you weigh too little or too much. The BMI calculator enables a calculation in seconds. However, there are a few things to consider when it comes to the BMI. If misinterpreted, it can even be dangerous. We will show you how to calculate your BMI, which BMI is normal and what you should know for a correct classification.

➠ Content: This is what awaits you

➠ Content: This is what awaits you

BMI calculator: calculate your BMI for free

The abbreviation BMI stands for the so-called body mass index, which is sometimes also referred to as the body mass index or body mass number. This is used as an indicator to evaluate a person's body weight in relation to their height. A BMI that is too high stands for overweight, while a BMI that is too low indicates that the person is underweight.

But how do I calculate the body mass index? The formula is very simple: body weight in kilograms divided by height in meters squared. Or represented graphically:

Use the BMI formula

A simple example to illustrate this:

  • Max Mustermann weighs 86 kilograms and is 1.80 meters tall.
  • For the BMI calculator you only need to find 86 divided by 3.24 (1.8 squared) - and the calculator gives you a body mass index of 26.5.
  • The BMI is always rounded to one decimal place.

Another example is a weight of 73 kilograms and a height of 1.72. This results in a BMI of 24.7.

BMI table: what kind of BMI is healthy?

With the BMI calculator you can now easily find out your own BMI. However, that is not enough to be able to interpret the BMI. For this purpose, the World Health Organization (WHO) has issued a classification that divides the BMI into a total of six categories:

  • BMI less than 18.5 means underweight
  • BMI from 18.5 to 24.9 means normal weight
  • BMI from 25.0 to 29.9 means pre-obesity (overweight)
  • BMI from 30.0 to 34.9 means grade 1 obesity
  • A BMI of 35.0 to 39.9 means grade 2 obesity
  • A BMI of more than 40 means grade 3 obesity

In the above examples, the first person with a BMI of 26.5 would fall into the pre-obesity category, while the second BMI of 24.7 corresponds to normal weight.

Which BMI for which age?

If you check your BMI regularly, you will notice changes immediately. If, on the other hand, it has been years or even decades since the BMI was last calculated, the result is a surprise for some - and sometimes a shock. As you get older, the BMI shows unexpectedly unhealthy tendencies, even though you actually feel good.

So did you suddenly become overweight or underweight in old age and should you start adjusting your diet as soon as possible? Not necessarily. The BMI applies generally to all adults, but differences between the age groups should not be ignored.

The human metabolism changes with age. This leads to weight changes. It is therefore quite normal for people between 40 and 60 years to weigh more on average than 20 or 30 year olds. Thus, the BMI also increases at this age, because of course the body size remains the same or sometimes even decreases a little. Experts therefore recommend using a different normal weight for each age group:

  • Between the ages of 35 and 44, a BMI of 21 to 26 is the ideal weight.
  • Between the ages of 45 and 54, a BMI of 22 to 27 is the ideal weight.
  • Between the ages of 55 and 64, a BMI of 23 to 28 is the ideal weight.
  • If you are over 65 years of age, a BMI of 24 to 29 is the ideal weight.

Even later in life, the body increasingly loses muscle mass, which in turn reduces body weight and BMI in old age. To conclude immediately that you are underweight would, however, ignore important factors here too.

BMI: Treat children and teenagers separately

The World Health Organization explicitly points out that the above classification using the BMI is designed for adults. However, the BMI calculator includes teenagers as well as children. However, two points must be observed here:

  • At a young age, the body is in constant development. For some, the thrust comes a little faster, for others a little later. The classification in the BMI for children is based on a comparison with average sizes and weights, which are only applicable to a limited extent. For example, if a child had an early growth spurt and is significantly taller than other children in the age group, the BMI is correspondingly skewed.
  • The World Health Organization publishes special tables for children's BMI, distinguishing between boys and girls. This is also due to the fact that the pace of developments in children varies between the sexes.

Parents and grandparents attach great importance to the healthy development of their children and grandchildren. The BMI can be used as a guide, but should not be overestimated or misinterpreted. If you feel that your grandson weighs too much or too little, you should advise parents to talk to a pediatrician. This can better classify and evaluate the development of the child. This also reduces the risk that parents will incorrectly classify a child's BMI and possibly change their diet, although this is not necessary at all.

BMI: are women and men different?

The BMI calculator for men basically also applies to women. However, this has nothing to do with equality, but with the fact that average values ​​are used as a basis.

This can lead to a distorted evaluation. Assuming, for example, that a BMI of 25 has the same meaning for men and women, ignores too many differences between the sexes.

Due to this fact, no different BMI calculator for women and men has become established in recent years, but at least a slightly changed BMI table for women. Here you can see which BMI means what for women:

  • BMI less than 19 means underweight
  • BMI from 19 to 23.9 means normal weight
  • BMI from 24.0 to 29.9 means overweight
  • BMI from 30.0 to 34.9 means grade 1 obesity
  • A BMI of 35.0 to 39.9 means grade 2 obesity
  • A BMI of more than 40 means grade 3 obesity

The shifts can only be seen in the lower area. This is why many experts have criticized this table, which basically does not take into account the different body types of women.

Criticism: Don't overestimate BMI

The BMI has been used as an indicator for several decades. However, there have been points of criticism and weaknesses behind the yardstick for just as long. Since the beginning of the use of the BMI, there has been discussion about whether it is even suitable for assessing individual people.

Some of the experts say: No, it isn't. Although the tables can be designed differently, the BMI calculator does not differentiate according to age or gender.

This can have a negative impact on the meaningfulness of the body mass index, because every body changes differently. An increasing or decreasing BMI does not have to be synonymous with being overweight or underweight in old age, but may only result from natural changes in the body.

BMI does not differentiate between fat and muscle mass

Another big point of criticism of the BMI: The value is based only on body weight, whereby it does not take into account how this is composed. Muscles are significantly heavier than adipose tissue, which means that a muscular and well-trained body can have a significantly higher BMI.

In such a case, the consideration of the body mass index has almost no meaningfulness, strength athletes often have a BMI of over 25 - but of course they are not overweight.

And not even fat is the same as fat. The BMI does not take into account whether it is dangerous belly fat or more harmless accumulations of fat.

Therefore, you should always take a critical look at the body mass index. Make sure you do your research and speak to a doctor before acting on a high BMI alone.

What other readers have read

[Photo credit: Rostislav Sedlacek by]