How to calculate BMI: what the result really means (2026)

Calculating BMI takes five seconds, but interpreting the result properly is another story. The Body Mass Index has been the standard for decades for assessing healthy weight, but in recent years there has been increasing criticism of its limitations. In this article we explain how to calculate your BMI, what the categories mean, where the figures fall short, and which alternatives often give a more complete picture.

What is BMI and how do you calculate it?

BMI stands for Body Mass Index and is a ratio between your weight and your height. The formula is simple:

BMI = weight in kilograms / (height in metres x height in metres)

An example: if you weigh 75 kilos and you are 1.80 metres tall, your BMI is 75 / (1.80 x 1.80) = 75 / 3.24 = 23.1.

The index was devised in the 19th century by the Belgian statistician Adolphe Quetelet and was originally called the Quetelet Index. It was not until the 1970s that researchers rediscovered it as a practical screening tool for large populations. The Voedingscentrum explains BMI clearly for the Dutch context.

BMI table: what do the categories mean?

The World Health Organization (WHO) uses four main categories for adults:

Within obesity, further distinctions are made between class 1 (30 to 35), class 2 (35 to 40) and class 3 (40 or higher). The WHO on BMI provides the international guidelines.

Important: this table applies to adults aged 18 to about 70 with an average body build and Northern European background. For children, older adults and people with a different ethnic background, different cut-offs apply.

Why BMI alone is not enough

BMI has a big advantage: it is fast, cheap and simple. But the formula looks only at total weight and says nothing about which tissues make up that weight. There are a few important limitations:

• Muscle mass is not distinguished from fat: a muscular strength athlete can have a BMI of 28 without any health risk.
• Fat distribution does not count: abdominal fat is much less healthy than fat on hips and thighs, but BMI cannot see the difference.
• Ethnicity: in people with an Asian background, risks already begin around BMI 23.
• Age: older adults often have less muscle and more fat at the same weight than younger people, and a slightly higher BMI is not always unhealthy for them.
• Sex: women on average have a higher body fat percentage at the same BMI than men.

If you are seriously working on your composition, it helps to do other measurements alongside BMI. If you are working on weight loss after 50, read losing weight after 50 for age-specific tips. For getting toned, getting lean after 40 and getting toned after 50 are practical routes.

Better alternatives and additions

If you want a fuller picture than just BMI, there are a few measurements that say more:

Waist circumference

This is the distance around your middle, at the narrowest point between your lowest rib and your hip bone. Cut-offs according to the RIVM health monitor:

• Men: up to 94 cm healthy, 94 to 102 cm raised risk, above 102 cm strongly raised risk.
• Women: up to 80 cm healthy, 80 to 88 cm raised risk, above 88 cm strongly raised risk.

Waist circumference is a good predictor of type 2 diabetes and cardiovascular disease, precisely because it measures abdominal fat.

Waist-to-height ratio

A handy rule of thumb: divide your waist circumference by your height (both in cm). If the result is below 0.5, you are generally on track. Above 0.6 there is clearly elevated risk.

Body fat percentage

With a skinfold caliper, bioimpedance scale or a DEXA scan, you measure what percentage of your weight is fat. For healthy adult men, that lies between 10 and 22 percent; for women between 20 and 32 percent.

Fitness and strength

How often you move and how strong you are often predicts your health better than your weight alone. Read how often per week to exercise for a sensible minimum.

BMI and your daily calories

If your BMI is heading towards overweight or obesity and you want to do something about it, your nutrition is decisive. Start by calculating your daily needs and aim for a small deficit.

• Calculate calorie needs in 2026 gives a step-by-step plan with Dutch data.
• Daily calories for women discusses women’s specific needs.
• High-carb foods: list and choices helps you make smart choices without cutting out whole food groups.

Combine that with regular movement and strength training to protect your muscle mass during weight loss.

When to see your GP

A deviating BMI is not in itself a reason to panic, but there are situations in which it is better to drop by your GP:

• BMI under 18.5 combined with fatigue, hair loss or menstrual disorders.
• BMI above 30, or BMI 25 to 30 with a large waist circumference.
• Rapid weight change without a clear cause (more than 5 percent in 6 months).
• BMI in the healthy zone but with complaints like shortness of breath, high blood pressure or high cholesterol.

If you have raised blood pressure, also read exercise and blood pressure. And if your resting heart rate stands out, resting heart rate of 40 provides context.

Want to get to work in a focused way with guidance? Through gyms near you you can find locations with personal trainers and coaches who can help.

Conclusion

Calculating BMI is a handy first check, but never the whole story. The formula does not take into account muscle mass, fat distribution, ethnicity or age. Always supplement your BMI with your waist circumference and look at your lifestyle as a whole: how you eat, how much you move and how strong and fit you are. If you are in doubt about the result or see striking changes, discuss it with your GP.