Health Calculators

BMI is a useful population-level screening tool, but it has limitations at the individual level. It does not distinguish between fat and muscle mass, so muscular individuals can be classified as overweight despite being lean. Older adults may have a normal BMI but high body fat percentage. BMI is best used alongside other measures such as waist circumference, body fat percentage, and clinical assessment.

BMR (Basal Metabolic Rate) is the calories your body burns at complete rest — the minimum needed to keep your organs functioning. TDEE (Total Daily Energy Expenditure) adds the calories burned through physical activity by multiplying BMR by an activity factor. TDEE is the figure most useful for weight management: eating below it creates a deficit, eating above it creates a surplus.

The Mifflin-St Jeor equation (1990) is generally considered the most accurate for the general population and is recommended by the American Dietetic Association. The older Harris-Benedict equation (1919, revised 1984) tends to overestimate slightly. For lean or muscular individuals, the Katch-McArdle formula, which uses lean body mass, may be more accurate.

A moderate calorie deficit of 500 kcal per day below your TDEE is the commonly recommended starting point, theoretically producing around 0.45 kg (1 lb) of fat loss per week. However, metabolic adaptation means the actual rate of loss slows over time. Very low calorie diets can lead to muscle loss and nutritional deficiencies. Always consult a registered dietitian or healthcare professional before making significant dietary changes.

General guidelines (American Council on Exercise): Essential fat: Men 2–5%, Women 10–13%. Athletes: Men 6–13%, Women 14–20%. Fitness: Men 14–17%, Women 21–24%. Acceptable: Men 18–24%, Women 25–31%. Obesity: Men 25%+, Women 32%+. These are general ranges — a qualified healthcare provider can assess body composition in the context of your overall health.

BMI calculators for adults use fixed thresholds that are not appropriate for children. Child BMI uses age- and sex-specific percentile charts (2nd–98th percentile ranges). Our BMI for age calculator uses the CDC growth charts for ages 2–19. For other health metrics such as calorie needs, children's requirements differ significantly from adults and should be guided by a paediatric dietitian.

The most widely used estimate is HRmax = 220 − age. This is a population average with high individual variability (±10–12 bpm). A more accurate formula for older adults is HRmax = 211 − (0.64 × age). For precise training zone definition, a supervised maximal exercise test provides the most reliable measurement.

No. Health calculators are informational and educational tools. They provide population-level reference ranges to help you understand your metrics and have more informed conversations with healthcare providers. They are not diagnostic tools and do not constitute medical advice. Always consult a qualified healthcare professional for medical decisions, diagnosis, or treatment planning.