How it's calculated
Basal Metabolic Rate is calculated using the Mifflin-St Jeor equation, generally considered the most accurate widely-used predictive formula. Total Daily Energy Expenditure (TDEE) is then estimated by multiplying BMR by an activity factor reflecting how much you move in a typical week.
Activity multipliers used for TDEE
| Activity level | Multiplier |
|---|---|
| Sedentary (little/no exercise) | 1.2 |
| Light activity (1–3 days/week) | 1.375 |
| Moderate activity (3–5 days/week) | 1.55 |
| Very active (6–7 days/week) | 1.725 |
| Extremely active (physical job or training) | 1.9 |
Clinical use
- BMR represents the energy your body needs at complete rest for basic functions like breathing, circulation, and cell repair — TDEE adds the energy used through daily activity and exercise on top of that.
- For weight loss, a common approach is a moderate calorie deficit below TDEE (e.g. 500 kcal/day, roughly 0.5 kg/week); for weight gain, a moderate surplus above TDEE.
- The Mifflin-St Jeor equation is now generally preferred over the older Harris-Benedict equation, having been shown to more accurately predict measured resting energy expenditure in modern validation studies.
- These formulas estimate average population relationships — individual metabolic rate can vary meaningfully due to muscle mass, genetics, thyroid function, and other factors, so treat the result as a starting estimate.
Frequently asked questions
What is BMR?
Basal Metabolic Rate is the number of calories your body needs at complete rest to maintain basic functions like breathing, circulation, and cell repair — it doesn't include any activity or exercise.
What is the difference between BMR and TDEE?
BMR is calories needed at rest; TDEE (Total Daily Energy Expenditure) adds the calories burned through daily activity and exercise on top of BMR, giving a more complete picture of total calorie needs.
How many calories should I eat to lose weight?
A common approach is eating somewhat below your TDEE — for example about 500 kcal/day less for roughly 0.5 kg (1 lb) of weight loss per week — though individual needs vary and sustainable, gradual changes are generally recommended over aggressive deficits.
Is the Mifflin-St Jeor equation accurate?
It's generally considered the most accurate widely-used predictive equation for resting energy expenditure in modern validation studies, more so than the older Harris-Benedict equation, though individual variation still exists.
References
- Mifflin MD, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51:241-247.
- Frankenfield D, et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. J Am Diet Assoc. 2005;105:775-789.
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids.