BMR calculator
Your basal metabolic rate (BMR) is the energy your body burns at rest just to stay alive. This calculator shows BMR from both the Harris-Benedict and Mifflin-St Jeor equations so you can compare estimates. It also explains how BMR differs from TDEE — total daily expenditure once activity is included — and displays maintenance calories at common activity levels.
Sex
Age (years)
Height (cm)
Weight (kg)
Result
Mifflin-St Jeor: 1451.5 kcal
Harris-Benedict: 1491.64 kcal
This result is informational only and does not replace medical advice.
How to calculate BMR
1. Enter sex, age, height, and weight.
2. View BMR results from Harris-Benedict and Mifflin-St Jeor side by side.
3. Select an activity level to see estimated TDEE (BMR × multiplier).
4. Use TDEE for maintenance planning, or open the calorie calculator for deficit/surplus targets.
BMR calculation examples
45-year-old man, 175 cm, 82 kg
Mifflin-St Jeor BMR ≈ 1,720 kcal; Harris-Benedict ≈ 1,780 kcal — often within 3–5%. At moderate activity (×1.55), TDEE lands near 2,670–2,760 kcal/day.
30-year-old woman, 160 cm, 60 kg
Mifflin-St Jeor BMR ≈ 1,310 kcal; Harris-Benedict ≈ 1,350 kcal. Sedentary TDEE (×1.2) ≈ 1,570–1,620 kcal; lightly active (×1.375) ≈ 1,800–1,860 kcal.
Why two formulas?
If Mifflin gives 1,650 kcal and Harris 1,710 kcal, averaging or preferring Mifflin (common in modern apps) is reasonable. Track weight for two weeks to see which maintenance estimate matches reality.
When to use this tool
• When you want BMR separate from activity before building a meal plan.
• When you compare Harris-Benedict vs Mifflin-St Jeor for coursework or coaching.
• When you explain to clients why rest-day calories differ from training days.
When to choose something else
• When you need macro targets and deficit presets — use the calorie calculator.
• When metabolic conditions (thyroid, etc.) affect expenditure — consult a physician.
• When indirect calorimetry lab measurement is required for clinical care.
Understanding the formulas
Harris-Benedict was among the first widely used BMR equations; Mifflin-St Jeor was validated on a more contemporary sample and is often preferred today. Both use height, weight, age, and sex because those predict resting metabolism in groups — not because they capture body composition directly. Athletes with high lean mass may need slightly higher calories than formulas suggest; older adults with low muscle may need less. Treat output as a structured guess, then validate with scale trends.
BMR in the bigger picture
BMR typically accounts for 60–75% of TDEE in sedentary people and a smaller share in very active ones. Crash dieting can lower BMR over time via adaptive thermogenesis. Sustainable plans rarely eat at or below BMR for long except under supervision. Knowing BMR helps you see the floor of your needs and why extremely low-calorie diets feel unsustainable — your organs alone demand substantial energy.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR is rest-only burn. TDEE includes BMR plus physical activity, NEAT (fidgeting, walking), and the thermic effect of food. TDEE is what you eat to maintain weight.
Which formula is more accurate?
Mifflin-St Jeor (1990) generally matches measured BMR slightly better in modern populations. Harris-Benedict (revised 1984) can run a bit higher. Neither is exact for every individual.
What activity multiplier should I pick?
Be honest: “moderately active” means regular exercise most days, not a desk job with one gym session. Overestimating activity is a common reason fat-loss stalls.
Does muscle mass change BMR?
Yes, but less than many think — a kilogram of muscle adds roughly 10–13 kcal/day at rest. Body size, age, and genetics still dominate.
Should I eat at BMR on rest days?
Usually no — unless TDEE is very low, eating only BMR creates a large deficit. Most people use average daily TDEE across the week.
Is my data sent to a server?
No. Calculations stay in your browser.
Is this tool free?
Yes. Unlimited use, no sign-up.