BMR Calculator
📜 BMR equation sources
Primary output uses Mifflin-St Jeor (1990), shown by comparative studies to predict measured RMR within 10% for most adults; Harris-Benedict (1919, revised 1984) and Katch-McArdle (lean-mass based) are provided for comparison. Reference: Academy of Nutrition and Dietetics evidence analysis. Last reviewed: June 2026.
📊 Methodology: This calculator uses validated clinical formulas as cited in the sources below. Results are estimates for general informational purposes. Consult a qualified healthcare professional before making health decisions.
What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain basic life functions: breathing, circulation, cell production, and nutrient processing. BMR typically accounts for 60-75% of your total daily calorie expenditure. This calculator uses the Mifflin-St Jeor equation, considered the most accurate BMR formula. — also see our TDEE calculator. Need to continue this calculation? Try the TDEE Calculator or the Calorie Calculator.
BMR vs TDEE
BMR only covers resting metabolism. Your Total Daily Energy Expenditure (TDEE) includes BMR plus calories burned through physical activity and digestion. To get your TDEE, multiply BMR by an activity factor: 1.2 for sedentary, 1.375 for light activity, 1.55 for moderate, 1.725 for active, and 1.9 for very active lifestyles.
Important health note
This calculator is for general information and self-checking only. It should not be used as a diagnosis, treatment plan, or replacement for advice from a qualified doctor, dietitian, trainer, or other healthcare professional. If you are pregnant, managing a medical condition, taking medication, recovering from illness, or making a major diet or exercise change, please speak with a professional before acting on the result.
How can you apply these results practically?
The BMR Calculator is built for people who want a fast answer without losing context. It keeps the calculation simple, shows the result clearly, and helps you understand what the number means before you use it in a real decision.
Nutrition calculators estimate daily energy needs from personal details and activity assumptions. They are helpful for planning, but real results depend on consistency, food tracking accuracy, training, sleep, and metabolism.
What BMR means and why it matters
Your Basal Metabolic Rate (BMR) is the minimum number of calories your body needs to sustain essential biological functions while completely at rest — no movement, no digestion, no activity of any kind. These functions include maintaining heart rate, breathing, body temperature, brain activity, cellular repair, and organ function. BMR accounts for approximately 60–70% of your total daily calorie expenditure, making it the largest single factor in your energy needs.
Understanding your BMR is the foundation of any calorie-based nutrition plan. Every calorie target — whether for fat loss, muscle gain, or maintenance — is calculated by starting with BMR and adjusting upward for activity and goal.
The Mifflin-St Jeor BMR formula
Multiple BMR equations exist. The Mifflin-St Jeor equation is the most widely validated for modern adults and is recommended by most nutrition and dietetics organisations:
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 — 40-year-old man, 80 kg, 175 cm:
BMR = (800 + 1093.75 – 200 + 5) = 1,699 calories/day
Example — 32-year-old woman, 62 kg, 163 cm:
BMR = (620 + 1018.75 – 160 – 161) = 1,318 calories/day
Other BMR formulas
- Harris-Benedict (1919, revised 1984): Older formula, tends to overestimate BMR by 5% in sedentary adults. Still widely used. Men: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) – (5.677 × age). Women: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) – (4.330 × age).
- Katch-McArdle: Uses lean body mass instead of total weight — most accurate for lean, muscular individuals. BMR = 370 + (21.6 × Lean Body Mass kg). Requires knowing body fat percentage to calculate lean mass.
What factors affect BMR?
- Body composition: Muscle tissue burns approximately 3× more calories at rest than fat tissue. People with higher muscle mass have higher BMRs at the same body weight.
- Age: BMR decreases approximately 1–2% per decade after age 30, primarily due to muscle mass loss (sarcopenia). This is why calorie needs decrease with age.
- Sex: Men generally have higher BMRs than women of the same age and weight due to higher average muscle mass and lower essential fat percentage.
- Thyroid function: The thyroid gland regulates metabolic rate. Hypothyroidism (underactive thyroid) can reduce BMR by 20–30%. Hyperthyroidism raises it.
- Genetics: Twin studies suggest 40–70% of BMR variation is genetically determined.
- Temperature: BMR increases slightly in cold environments as the body generates more heat to maintain core temperature.
From BMR to TDEE and calorie targets
BMR represents your needs at complete rest. To find your Total Daily Energy Expenditure (TDEE) — what you actually need — multiply BMR by an activity factor:
- Sedentary: BMR × 1.2
- Lightly active (1–3 workouts/week): BMR × 1.375
- Moderately active (3–5 workouts/week): BMR × 1.55
- Very active (6–7 workouts/week): BMR × 1.725
For the 40-year-old man (BMR 1,699) who is lightly active: TDEE = 1,699 × 1.375 = 2,336 calories/day. For fat loss: 2,336 – 400 = 1,936 calories/day.
Why BMR decreases with age and how to counter it
BMR drops approximately 1–2% per decade after age 30, primarily due to loss of muscle mass (sarcopenia). A 60-year-old who weighs the same as they did at 30 may have lost 5–8 kg of muscle, replacing it with fat — causing their BMR to be 100–160 kcal lower per day. The most effective counter: resistance training 2–3 times per week. Each kg of muscle added raises BMR by approximately 13 kcal/day — meaningful over years of consistent training.
BMR differences between individuals at the same weight
Two people weighing 70 kg can have BMRs differing by 200+ kcal/day based on: muscle mass (higher = higher BMR), genetics (thyroid function, mitochondrial efficiency), height (taller people have more surface area, slightly higher BMR), and sex (men average 5–10% higher BMR than women at the same weight due to higher muscle proportion). The Mifflin-St Jeor formula accounts for weight, height, age, and sex — it is the most accurate formula available without a metabolic test.
Mifflin-St Jeor vs Harris-Benedict: which is more accurate?
The Mifflin-St Jeor equation (1990) consistently outperforms the original Harris-Benedict equation (1919) in accuracy studies. A 2005 meta-analysis in the Journal of the American Dietetic Association found Mifflin-St Jeor predicted BMR within 10% for 82% of non-obese individuals. Harris-Benedict overestimates BMR by 5–15% in sedentary individuals. iCalcApp uses the Mifflin-St Jeor equation. For clinical nutrition, the Ireton-Jones or Penn State equations are used for hospitalised patients.
How muscle mass directly affects BMR: the numbers
Muscle tissue burns approximately 13 kcal/kg per day at rest; fat tissue burns only 4.5 kcal/kg per day. A person with 60 kg lean mass and 10 kg fat mass has a resting metabolic rate contribution of (60×13) + (10×4.5) = 780 + 45 = 825 kcal from these tissues alone. Adding 5 kg of muscle through strength training increases daily BMR by approximately 65 kcal — equivalent to a 20-minute walk. This is why muscle mass is the most effective long-term metabolism booster.
Health disclaimer: This calculator provides estimates for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Results are based on population averages and may not apply to individuals with specific health conditions. Always consult a qualified healthcare professional. Reviewed by Dr. P Nair, MBBS, MD.
Frequently asked questions about BMR
Can I increase my BMR? Yes. Building muscle through resistance training is the most effective long-term strategy — each kilogram of additional muscle burns approximately 13 extra calories per day at rest. High protein intake (due to thermic effect) and avoiding extreme calorie restriction also preserve metabolic rate.
Is it harmful to eat at or below BMR? Consistently eating below BMR for extended periods risks nutrient deficiency, muscle loss, hormonal disruption, and metabolic adaptation. BMR is the floor — sustained intake should generally remain at or above this level.
Why does my weight loss slow after a few weeks? As body weight decreases, BMR decreases because a lighter body has less tissue to maintain. Recalculate BMR and TDEE every 4–6 weeks during a fat loss phase to update your calorie target accordingly.
Sources & References
- Mifflin MD et al. — New Predictive Equation (1990) — Primary equation: 10×weight + 6.25×height − 5×age ± 5/161; validated as most accurate for most adults
- Academy of Nutrition and Dietetics — Evidence Analysis — Comparative accuracy analysis of Harris-Benedict vs Mifflin-St Jeor equations
Average BMR by age and gender (Mifflin-St Jeor, 170cm / 70kg)
| Age | Male BMR (kcal/day) | Female BMR (kcal/day) |
|---|---|---|
| 20–25 | ~1,870 | ~1,540 |
| 30–35 | ~1,830 | ~1,500 |
| 40–45 | ~1,790 | ~1,460 |
| 50–55 | ~1,750 | ~1,420 |
| 60–65 | ~1,710 | ~1,385 |
| 70+ | ~1,650 | ~1,340 |
Activity multipliers for calculating TDEE from BMR
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | BMR × 1.2 |
| Lightly active | Light exercise 1–3 days/week | BMR × 1.375 |
| Moderately active | Moderate exercise 3–5 days/week | BMR × 1.55 |
| Very active | Hard exercise 6–7 days/week | BMR × 1.725 |
| Extra active | Physical job + hard training twice daily | BMR × 1.9 |
Related calculators
⚕️ Medical disclaimer: This calculator provides educational estimates only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. Formulas and reference ranges follow WHO and ICMR published guidelines — see our methodology.
How does this differ from the TDEE and Calorie calculators?
BMR (this page) is your burn at complete rest — the metabolic baseline. To include daily activity and exercise, the TDEE calculator applies activity multipliers; to turn that into what you should actually eat for weight loss or gain, use the calorie calculator.