What Is BMR and How Do You Calculate It?
📅 12 July 2026 · ⏱ 8 min read · Keywords: what is BMR, how to calculate BMR
Even if you spent all day in bed doing absolutely nothing, your body would still burn energy: your heart beats, your lungs breathe, your brain works, your cells renew. That background bill is your basal metabolic rate (BMR) — and it's the single largest item in your daily calorie budget. Whether you want to lose, gain or maintain weight, the maths starts here.
What Exactly Does BMR Measure?
BMR is your body's vital energy need at complete rest. Your total daily expenditure (TDEE) breaks down like this:
| Component | Share | What it is |
|---|---|---|
| BMR | ~60–70% | Vital functions: organs, cell renewal, body temperature |
| NEAT | ~15–20% | Non-exercise movement: walking, standing, fidgeting |
| Exercise | ~5–10% | Deliberate workouts — a surprisingly small slice for most people |
| TEF | ~10% | Energy used to digest food (protein costs the most) |
So when we say "my metabolism is slow", we're mostly talking about BMR — and exercise plays a smaller role than most people assume. For a deeper dive into how the three key numbers relate, see BMR vs TDEE vs BMI.
How to Calculate BMR: the Mifflin-St Jeor Equation
Developed in 1990 and recommended by the Academy of Nutrition and Dietetics among others, Mifflin-St Jeor is the most accurate of the practical formulas:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Example: a 30-year-old man, 175 cm (5'9"), 80 kg (176 lb):
10×80 + 6.25×175 − 5×30 + 5 = 800 + 1,093.75 − 150 + 5 ≈ 1,749 kcal/day
Skip the arithmetic with the free BMR calculator — it gives you the number in seconds. For your total daily needs, the calorie (TDEE) calculator factors in your activity level too.
What Changes Your BMR?
- Muscle mass (the big one): muscle burns several times more energy at rest than fat. Of two people at the same weight, the more muscular one has a clearly higher BMR.
- Age: BMR drops ~2–3% per decade, largely through muscle loss — but that's not destiny; strength training slows it dramatically.
- Sex: men carry more muscle on average, hence the +5 / −161 difference in the formula.
- Hormones: thyroid hormone directly sets metabolic speed; hypothyroidism lowers BMR.
- Crash-diet history: prolonged very-low-calorie eating suppresses BMR through adaptive thermogenesis.
Can You Actually Speed Up Your Metabolism?
For detox teas and "fat-burner" pills, the short answer is no — there's no proven lasting effect. What genuinely works:
- Build muscle: 2–3 strength sessions a week is the only proven way to raise BMR permanently. No gym needed — start with the full-body home workout.
- Eat more protein: protein's digestion cost (TEF) is 20–30% — triple that of carbs — and it protects muscle. Get your target from the protein calculator.
- Grow your NEAT: daily steps, stairs, standing work… the difference-maker is usually daily movement, not the gym hour.
- Avoid starvation diets: chronically eating far below BMR suppresses your metabolism. For a safe pace, read how much weight you can safely lose in a month.
Summary
- BMR = energy burned at complete rest; 60–70% of your daily total.
- Best practical formula: Mifflin-St Jeor (10×kg + 6.25×cm − 5×age; men +5, women −161).
- Set weight goals against your TDEE, not your BMR — BMR is your safe floor.
- The only thing that permanently raises BMR is muscle mass — not detox products.