What is BMR?
Basal Metabolic Rate (BMR) is the energy your body uses at complete rest in a temperate environment when the digestive system is inactive — often approximated after many hours without food. It covers the cost of vital organs, brain, heart, kidneys, muscle upkeep, and temperature regulation, before deliberate movement or digesting a meal.
True lab BMR needs strict conditions (rested, fasted, thermoneutral, unstressed). Online calculators use population equations — practical estimates, not indirect calorimetry.
Why BMR matters
Resting metabolism is often the largest slice of daily burn — commonly cited as on the order of ~70% of total expenditure for many people, with activity and the thermic effect of food making up the rest. That is why size, muscle, and age move your baseline so much.
How this BMR calculator works
Pick an equation in + Settings (default Mifflin–St Jeor). We multiply your BMR by standard activity factors to show TDEE (maintenance calories) for each lifestyle row in the results table.
Mifflin–St Jeor (recommended for most)
- Men: BMR = 10W + 6.25H − 5A + 5
- Women: BMR = 10W + 6.25H − 5A − 161
W = kg, H = cm, A = years.
Revised Harris–Benedict
- Men: BMR = 13.397W + 4.799H − 5.677A + 88.362
- Women: BMR = 9.247W + 3.098H − 4.330A + 447.593
Katch–McArdle
BMR = 370 + 21.6 × (1 − F) × W, with F = body fat as a decimal. Best when you know body fat from calipers, BIA, or our Body Fat Calculator.
Which formula should I use?
- Mifflin–St Jeor — strong default for general adults when you do not have body-fat data.
- Harris–Benedict — still seen in older materials; slightly different bias than Mifflin for modern populations.
- Katch–McArdle — lean or trained people with a reasonable body-fat % often get more sensible resting estimates.
Daily calorie needs by activity (multipliers)
TDEE ≈ BMR × multiplier. Be honest about desk time vs training — most people are less active than they think.
| Activity level | Multiplier |
|---|---|
| Sedentary: little or no exercise | 1.2 |
| Exercise 1–3 times/week | 1.375 |
| Exercise 4–5 times/week | 1.4648 |
| Daily exercise or intense exercise 3–4 times/week | 1.55 |
| Intense exercise 6–7 times/week | 1.725 |
| Very intense exercise daily, or physical job | 1.9 |
- Exercise: ~15–30 minutes elevated heart rate.
- Intense exercise: ~45–120 minutes elevated heart rate.
- Very intense exercise: ~2+ hours elevated heart rate.
Factors that affect BMR
- Muscle mass — the main lever you can train; more lean tissue raises resting burn.
- Age — tends to reduce BMR partly through muscle loss.
- Genetics — real person-to-person spread remains after accounting for size and composition.
- Temperature & fever — heat and cold both can raise expenditure.
- Dieting history — prolonged severe restriction can lower measured expenditure.
- Pregnancy, thyroid, caffeine/meds — can shift metabolism meaningfully.
BMR vs RMR
RMR (resting metabolic rate) is measured under relaxed but less strict conditions than BMR and is often a bit higher because of posture, recent food, and light autonomic tone. In everyday language the terms are often used interchangeably; this tool estimates BMR via equations, not a chamber test.
Using BMR for goals
- Fat loss: aim below TDEE, not necessarily below BMR; very low intakes need medical oversight.
- Maintenance: eat near the TDEE row that matches your real week.
- Muscle gain: modest surplus with progressive resistance training.
Limitations & professional testing
Equations cannot capture every individual. Indirect calorimetry (metabolic carts) measures oxygen/carbon dioxide exchange and can refine targets when precision matters. A classic reference discussing residual variance in BMR is Johnstone et al., American Journal of Clinical Nutrition, 2005.
For full targets with zigzag examples and a food-energy converter, see the Calorie Calculator.