The calculators in this section are about energy balance and body composition — the numbers behind why weight changes the way it does. They build on each other in a specific order: basal metabolic rate is the energy your body burns at complete rest, total daily energy expenditure adds movement and exercise on top of that, and body fat percentage describes what the resulting weight is actually made of rather than just what it totals.
Calculators in this section
Anion gap
BMI
BMI
BMI (NHS)
BMR
Body fat percentage
Body surface area
Calorie deficit
Calorie deficit
Calories to lose weight
Creatinine clearance
Fat free mass
Fibre intake
Heart age
Ideal body weight
Keto macros
Lean body mass
Mean arterial pressure
Next period
Protein intake
Pulse pressure
QALY
QRISK
Resting metabolic rate
Sodium intake
TDEE
Waist to height ratio
Waist to hip ratio
Water intake
Weight loss percentage
eGFR
None of these figures are exact measurements. BMR and TDEE come from population-average equations (Mifflin-St Jeor and its activity multipliers) rather than a direct reading of your own metabolism, and body fat from tape measurements is an estimate, not a DEXA scan. Used together, though, they give a far more useful picture than any single number on a bathroom scale — weight alone cannot tell you whether a change came from fat, muscle or water.