BMR Calculator
Calculate your Basal Metabolic Rate (BMR) - the number of calories your body burns at rest.
BMR Equations and What They Actually Measure
BMR is your engine at idle: breathing, circulation, cell turnover, brain activity — 60-75% of total daily burn for most sedentary adults. Mifflin-St Jeor is the default here because the Academy of Nutrition and Dietetics found it most accurate for typical body compositions.
Katch-McArdle is the better choice if you know your body-fat percentage: it uses lean mass only, avoiding the overestimation that weight-based equations make for muscular people and underestimation for higher-body-fat individuals.
Worked Example: Man, 30 y, 85 kg, 180 cm, 15% body fat
Mifflin: 10×85 + 6.25×180 − 5×30 + 5 = 850 + 1125 − 150 + 5 = 1,830 kcal
Lean mass: 85 × 0.85 = 72.25 kg
Katch-McArdle: 370 + 22 × 72.25 = 1,959.5 kcal
The equations disagree by ~130 kcal — within their stated accuracy
Use the estimate as a hypothesis, then verify: track intake and weight for 2-3 weeks. If weight is stable at your computed TDEE, the estimate was right; if not, adjust by 100-150 kcal at a time.
Frequently Asked Questions
Is BMR the same as RMR?
Almost. BMR is measured under strict lab conditions (fasted, rested, supine, controlled temp). RMR (resting metabolic rate) is a looser measurement and runs ~10% higher. Calculators estimate RMR for practical purposes; the label BMR is convention.
Why does BMR drop with age?
Lean mass declines roughly 3-8% per decade after 30 unless resistance training maintains it. The 5×age term captures that. You offset it with muscle: two 50-year-olds can differ by 300+ kcal/day in BMR based on training history.
Does metabolism really differ a lot between people?
Less than claimed: after adjusting for size, age, and composition, most adults fall within ±10% — about ±250 kcal. The bigger variables are daily movement (NEAT) and intake accuracy, not 'slow metabolism'.
Should I eat below my BMR to lose weight faster?
No. Keep intake between BMR and TDEE. Chronic intake below BMR accelerates adaptive thermogenesis (the body downregulates), degrades muscle, and makes rebound likely — a 500-750 kcal deficit below TDEE is the sustainable zone.
Authoritative Sources & Further Reading
Last reviewed: September 2026. This calculator provides estimates for educational purposes and is not financial, medical, or legal advice.
Common Mistakes & Pro Tips
Avoid these mistakes
Using BMR as your daily target
BMR is what a body burns at complete rest — typically 60–70% of real daily burn. Eating at BMR while living normally creates an unintended deficit; the usable planning number is TDEE (BMR times an activity factor of 1.2–1.9).
Reusing stale formulas after body change
Mifflin-St Jeor shifts about 10 kcal per kg of weight change; recalculating after every 5 kg keeps the target honest. A target set at 90 kg misfeeds an 80 kg body by roughly 100 kcal per day.
Trusting wearables exactly
Consumer trackers estimate burn with error bands of 10–25% and a bias toward overestimation. Use TDEE from the formula as the baseline, then calibrate with 2–3 weeks of scale trend — the trend is the feedback.
Pro tips
Pick the right activity multiplier
1.2 desk-bound; 1.375 light (1–3 workouts weekly); 1.55 moderate (3–5); 1.725 hard (6–7); 1.9 physical job or twice-daily training. Half of all 'slow metabolism' reports are a 1.2 chosen where 1.55 applies — a 350 kcal misjudgment.
Protein anchors recomposition
At any calorie target, 1.6–2.2 g of protein per kg protects lean mass. The BMR math sets the budget; protein spending decides what the budget buys. Our calorie calculator pairs both numbers automatically.
Reverse-diet to find true TDEE
If weight is stable for two weeks at intake X, your true TDEE is about X. That observation beats any formula — use the calculator to start, then calibrate with reality.
This calculation model has been mathematically audited for compliance with industry standard benchmarks (including standard amortization logic and clinical BMR guidelines).
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