For many, the body mass index (BMI) is as helpful a tool as the calorie calculator to keep an eye on their own weight and achieve goals related to their body. What many don't know, however, is that BMI changes with age. Our bodies are in a constant state of change throughout our lives. In this way, body shape changes repeatedly over time. The same applies to the composition of fat and muscle mass. You can find out what this means for BMI and what you need to pay attention to depending on your age in this article.
What is the body mass index?
BMI is a measure that evaluates body weight in relation to a person's height . However, it only serves as a rough guide, as the formula does not take into account either body shape or the composition of muscle and fat. In most cases, gender is not included in the calculation.
The body mass index was
The BMI can be calculated using a simple formula: body weight in kilograms (kg) divided by height in meters squared .
What does BMI say?
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 Organization (WHO), the B ody mass index is divided into different levels . The categories range from severely underweight to obesity type III.
| BMI value | Category |
| < 16.0 | severe underweight |
| 16.0 – 17.0 | Moderately underweight |
| 17.0 -18.5 | Slightly underweight |
| 18.5 -24.9 | Normal weight |
| 25.0-29.9 | Pre-obesity |
| 30.0-34.9 | Grade I obesity |
| 35.0-39.9 | Grade II obesity |
| ≥ 40 | Grade III obesity |
Even if the result is often used as a guideline to conclude on 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 yields an extreme value in the upper or lower range of the scale, this may well entail a certain risk of secondary diseases . For example, obese people are more likely to develop type 2 diabetes or cardiovascular disease and are more likely to have a stroke.
How does BMI develop in old age?
The body mass index serves as an indication of whether a person is of normal weight or is 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 should be noted:
The BMI for children and adolescents
Since the ratio between height and weight is constantly changing at the beginning of our lives, the classic BMI calculator is not suitable for people under the age of 18. In addition to height and gender, the body fat percentage must also be included in the calculation, which is why there is a separate BMI calculator for children .
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 ensure that the weight of the youngest is within the normal range, it is best to contact the pediatrician you trust.
Ideal weight for adults
As soon as the growth stops in adolescents, their body mass index can be determined with the help of the generally 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), a distinction can also be made according to gender. Accordingly, the ideal BMI value for men is between 20 and 25. For women, the normal weight is between 19 and 24. Athletes are an exception. Due to their high muscle percentage, different rules apply to them.
The BMI for seniors
The measured value is not only error-prone at a young age, but also with advancing age. Over the course of life, body composition changes. Thus, the fat percentage increases, while the muscle mass decreases.
For this reason, the categories need to be adjusted a little for those aged 65 and older. For older adults, a higher BMI and a few extra pounds are recommended. If it comes to a disease that weakens the body, additional fat reserves can indeed be useful. For more details, see BMI for women over 60 .
