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Health Calculators

Health and wellness: body mass index and ideal weight.

TheCalculator's health calculators provide quick references on your body composition and daily energy needs, based on validated clinical formulas. The Body Mass Index (BMI) follows World Health Organisation classification criteria and the calorie calculator uses the Mifflin-St Jeor equation (1990), considered the most accurate for non-elite-athlete adults according to current scientific evidence.

One thing should be stressed before using these calculators: they all provide estimates based on population formulas, not diagnoses. BMI was designed to study populations and does not distinguish muscle from fat; calorie and maximum heart rate formulas show individual deviations of up to 10% or more between people of the same age and build. They are useful as a starting point and for tracking your own progress over time, but any significant decision about your diet, your training or your health should be discussed with a healthcare professional.

BMI Calculator
Calculate your Body Mass Index and find your weight category.
Calorie & BMR Calculator
Calculate your BMR and daily calorie needs by activity and goal.
Maximum Heart Rate Calculator
Calculate your MHR and five training zones to optimise your workouts.
Daily Water Intake Calculator
Find out how much water you should drink per day based on your weight and activity.

Frequently asked questions

No. The results are indicative and are based on statistical averages for the general population, not your individual medical history. BMI, for example, does not distinguish muscle mass from body fat and does not account for factors such as age, sex or fat distribution. For nutritional diagnosis, treatment or personalised diet, always consult your doctor or a registered dietitian.

BMI only measures the ratio between weight and height, without distinguishing between muscle and fat. A very muscular person can have a BMI in the 'overweight' or even 'obese' category while being completely healthy and having a low body fat percentage. To assess body composition more accurately, health professionals use other metrics such as body fat percentage, waist circumference or bioelectrical impedance.

Under no circumstances. They are informational tools based on formulas validated for the general population, but they do not assess your medical history, your medication, your blood tests or specific conditions that completely change the recommendations, such as pregnancy, diabetes, kidney failure or heart disease. If you have any doubt about your weight, your diet, your hydration or the intensity at which you can safely train, consult your GP, a registered dietitian or a sports medicine specialist.

Because several validated formulas exist for the same quantity and each was derived by studying different populations. For maximum heart rate, the classic '220 − age' coexists with the more accurate Tanaka formula; for energy expenditure there are Mifflin-St Jeor, Harris-Benedict and Katch-McArdle, the latter also requiring your body fat percentage. Differences between them can reach 10%. What matters is not which gives the most favourable number, but always using the same formula so you can track your progress consistently over time.

No. All the calculators in this section are designed for adults. In under-18s, BMI is not interpreted with the WHO's fixed adult ranges but through percentiles adjusted for age and sex, because body composition changes markedly during growth. The same applies to calorie and hydration needs, which depend on the stage of development. To assess a child's or adolescent's health you must always use paediatric charts and consult their paediatrician.