Step 1: Basal metabolic rate (BMR)
BMR is the energy your body needs at complete rest to breathe, circulate blood and run its organs. We offer three well-known equations. Weight is in kg, height in cm and age in years.
Mifflin-St Jeor (default)
Men: BMR = 10 × weight + 6.25 × height − 5 × age + 5
Women: BMR = 10 × weight + 6.25 × height − 5 × age − 161
Validated against measured data, this is generally considered the most reliable for the general adult population.
Revised Harris-Benedict
Men: 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
Women: 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age
Katch-McArdle
BMR = 370 + 21.6 × lean body mass (kg)
Best when you know your body fat percentage, since it accounts for muscle mass. Lean body mass is weight × (1 − body fat %).
Step 2: Activity multiplier
Your BMR is multiplied by a factor from 1.2 (sedentary) to 1.9 (extra active) to estimate TDEE. See the full activity levels guide.
Worked example
A 35-year-old woman, 168 cm and 70 kg, lightly active:
- BMR = 10×70 + 6.25×168 − 5×35 − 161 = 1,414 Cal (5,916 kJ)
- TDEE = 1,414 × 1.375 = 1,944 Cal (8,134 kJ)
Goal targets
One kilogram of body fat holds roughly 7,700 Cal (32,200 kJ). We convert your desired weekly change into a daily adjustment: 0.25 kg per week is about 275 Cal a day and 0.5 kg per week is about 550 Cal a day. Targets never drop below 1,200 Cal (women) or 1,500 Cal (men).
Limitations
These are population-based estimates. Genetics, muscle mass, medications, sleep and hormones all shift real-world expenditure. Treat the result as a starting point and adjust from actual weight trends. The calculator is for healthy adults 18+ and is not a substitute for advice from a GP or Accredited Practising Dietitian.