BMR Calculator
Result Summary
No results yet
Enter your details and hit “Calculate” to see your results.
About BMR
Every calorie plan starts here whether it says so or not: BMR is the floor of your energy budget — what you'd burn in bed all day — and every “calories to lose weight” number is built by multiplying it up for activity and subtracting a deficit. Know the floor and the rest of the arithmetic stops being mysterious.
Enter sex, age, height, and weight for your BMR, the per-hour resting burn, and the equation's working. The number is the input to everything else: multiply by an activity factor for maintenance (that's TDEE), then adjust for goals.
The full daily-burn version with activity built in is the TDEE Calculator
The Mifflin-St Jeor Equation
One linear equation, sex adjusting only the constant:
Men: BMR = 10×kg + 6.25×cm − 5×age + 5 Women: BMR = 10×kg + 6.25×cm − 5×age − 161
Worked example: a 30-year-old man, 175 cm and 70 kg: 700 + 1,093.75 − 150 + 5 = 1,649 kcal/day — about 69 kcal per hour of just existing. The same stats female: 1,483. Mifflin et al. validated it against measured resting expenditure in 1990 (cited below); dietetic practice adopted it as the default.
From BMR to Daily Calories
Multiply BMR by an activity factor for maintenance calories — the standard multipliers on the worked example's 1,649:
| Lifestyle | Factor | Maintenance (example) |
|---|---|---|
| Sedentary (desk, little exercise) | 1.2 | 1,979 kcal |
| Light (1–3 workouts/week) | 1.375 | 2,267 kcal |
| Moderate (3–5 workouts/week) | 1.55 | 2,556 kcal |
| Active (6–7 workouts/week) | 1.725 | 2,845 kcal |
| Very active (physical job + training) | 1.9 | 3,133 kcal |
Most people overestimate their factor by one tier — an office worker who trains three evenings is “light-to-moderate,” not “active.” When in doubt, pick lower and adjust to results.
What Moves Your BMR
The levers, in order of practical size: body weight itself (each kg is ~10 kcal/day in the equation — weight loss genuinely lowers BMR), muscle mass (the biggest lever you control — muscle burns more at rest than fat, which is why resistance training protects metabolism during dieting), age (the −5/year term reflects gradual decline, much of it muscle loss rather than time itself), and sex differences in composition.
What doesn't meaningfully move it: metabolism-boosting foods and supplements (effects are trivial or transient), meal timing, and “starvation mode” as popularly imagined — severe restriction does trigger adaptive slowing, but of modest size. If a measured or suspected BMR sits far off the estimate, thyroid function is the medical question worth asking.
Frequently Asked Questions
What is a normal BMR?
Most adult BMRs land between about 1,200 and 2,000 kcal/day, scaling with size, muscle, sex, and age — a 70 kg, 175 cm, 30-year-old man estimates 1,649. There's no single “good” number; it's the floor of YOUR energy budget.
Is BMR the calories I should eat?
No — BMR is your at-rest floor. Eating at BMR is already a deficit for anyone who moves at all. Maintenance = BMR × activity factor (1.2–1.9); weight-loss plans subtract from THAT, and dropping below BMR for long stretches is a clinician conversation, not a default.
Why Mifflin-St Jeor instead of Harris-Benedict?
Harris-Benedict (1919) was built on a small early-1900s sample and overestimates modern adults; Mifflin-St Jeor (1990, cited below) re-derived the equation on contemporary data and validation studies favor it — which is why dietetic practice made it the default.
How accurate is the estimate?
Within roughly ±10% for most adults. It runs low for very muscular bodies and high for very lean-mass-poor ones, since it can't see composition. Katch-McArdle (based on lean mass) suits athletes who know their body-fat %; for everyone else Mifflin is the standard.
Does BMR drop when I lose weight?
Yes, mechanically: each kilogram carries about 10 kcal/day in the equation, so losing 10 kg lowers BMR ~100 kcal/day — plus some adaptive slowing during active dieting. Recalculate as your weight changes and keep lifting so the loss is fat, not the muscle that holds your BMR up.
BMR vs RMR — what's the difference?
BMR is measured under strict lab rest conditions; RMR (resting metabolic rate) allows normal conditions and runs slightly higher. Equations like Mifflin-St Jeor technically predict REE/RMR, and everyday usage — including this page — treats the terms interchangeably.
Sources & References
- [1]Mifflin, M.D. et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals — American Journal of Clinical Nutrition / PubMed
Methodology. This calculator uses formulas and health categories recognized by the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC). It is reviewed and maintained by the Vast Calculators editorial team.
Last updated · July 11, 2026
Disclaimer. This tool provides estimates for general informational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider before making decisions about your health.