For many, the body mass index (BMI) is just as helpful a tool as the calorie calculator for keeping track of one’s weight and achieving goals around one’s body. What many people don’t know, however, is that BMI changes with age. Our bodies are in a state of flux throughout our lives. For example, over time, the shape of the body changes again and again. The same applies to the composition of fat and muscle mass. In this article you will learn what this means for your BMI and what you need to pay attention to depending on your age.

What is the Body Mass Index?

The BMI is a measurement that assesses a person’s body weight in relation to their height. However, it only serves as a rough guide because the formula does not take into account body shape or the composition of muscle and fat. In most cases, gender is also not included in the calculation.

BMI berechnen

The body mass index was invented by the Belgian mathematician Adolphe Quetelet with the aim of developing an equation that depicts people in a normal distribution. He succeeded by calculating the relationship between weight and height. Soon after, however, the formula was no longer used to describe what was “normal”, as Quetelet intended. Instead, it was used as a yardstick to determine overweight.

BMI can be calculated using a simple formula: Body weight in kilograms (kg) divided by height in metres squared.

What does BMI mean?

Now that you know your BMI thanks to our free BMI calculator, you’re probably wondering what the calculated value actually means.

As the table below shows, according to the World Health Organisation (WHO), the body mass index is divided into different levels. The categories range from severe underweight to obesity type III.

BMI-valuecategory
< 16,0severe underweight
16,0 – 17,0moderate underweight
17,0 -18,5slightly underweight
18,5 -24,9normal weight
25,0-29,9 preadiposity
30,0-34,9obesity grade I
35,0-39,9obesity grade II
≥ 40obesity grade III

Even though the result is often used as a guideline to draw conclusions about a person’s health, this conclusion is actually not correct. This approach should be viewed critically, especially in the middle categories. If, on the other hand, the calculation spits out an extreme value in the upper or lower range of the scale, this can certainly entail a certain risk of secondary diseases. For example, obese people are more likely to develop type 2 diabetes or cardiovascular diseases and are more likely to suffer a stroke.

How does BMI develop in old age?

The body mass index serves as a guide to whether a person is of normal weight or affected by overweight or underweight, which in some cases requires treatment. However, the values as we know them may not be calculated and interpreted in the same way across all age groups. The following must be taken into account:

BMI Rechner für Kinder
Since the classic BMI calculator is not suitable for children, a separate BMI calculator was developed for the youngest.

Also important to know: The calculation only makes sense for children from the age of eight. Due to baby fat and growth spurts, the weight of smaller children can fluctuate greatly. If you want to be sure that the weight of your little ones is within the normal range, it is best to consult your paediatrician.

Ideal weight for adults

As soon as growth stops in adolescents, their body mass index can be determined with the help of the commonly known BMI calculator. The BMI table above is used for interpretation. The guidelines apply to everyone between the ages of 19 and 65.

According to the German Nutrition Society (DGE), an additional distinction can be made according to gender. According to this, the ideal BMI value for men is between 20 and 25. For women, the normal weight is between 19 and 24. Female athletes are an exception. Due to their high muscle content, other rules apply to them.

The BMI for seniors

The measurement is not only prone to error when you are young, but also with advancing age. In the course of life, the body composition changes. For example, the fat percentage increases, while the muscle mass decreases.

BMI für Ältere

For this reason, the categories need to be adjusted a little from the age of 65. For older people, a higher BMI and a few extra kilos on the ribs is definitely recommended. After all, if an illness occurs that weakens the body, additional fat reserves are indeed useful.