Estimate Basal Metabolic Rate using the Mifflin-St Jeor equation. Calories you burn at rest.
A free, in-browser Basal Metabolic Rate (BMR) calculator using the Mifflin-St Jeor equation — widely regarded as the most accurate BMR estimate for healthy adults. Enter your height, weight, age, and sex to see the calories your body burns at complete rest. Everything runs locally in your browser — your measurements are never uploaded.
Enter your height and weight
Switch between metric (cm, kg) and imperial (ft/in, lb) with the toggle. Measure without shoes, first thing in the morning for the most consistent reading.
Enter your age and sex
Age in full years. Biological sex is used for the ±5 / −161 constant in the Mifflin-St Jeor equation.
Read your BMR
The result updates live in kcal/day. This is the energy you would burn if you stayed in bed all day — anything you do beyond that adds on top.
BMR (Basal Metabolic Rate) is the energy your body burns at complete rest just to keep vital organs running. TDEE (Total Daily Energy Expenditure) adds the calories you burn through daily movement and exercise — typically BMR × 1.2 to 1.9 depending on activity level.
The original Harris-Benedict equation (1919) was derived from a small cohort and tends to overestimate BMR in modern populations. Mifflin-St Jeor (1990) used a larger, more diverse sample and is about 5% more accurate on average — it's now the recommended equation by the American Dietetic Association.
For healthy adults aged 19–78, Mifflin-St Jeor predicts resting energy expenditure to within roughly ±10% for about 80% of people. Accuracy drops for the elderly, competitive athletes with very high muscle mass, and people with obesity above BMI 40. For clinical precision, indirect calorimetry is the gold standard.
No. Every calculation runs in your browser. Your height, weight, age, sex, and BMR are never sent to a server.
The Mifflin-St Jeor equation was published in 1990 in the American Journal of Clinical Nutrition by Mifflin, St Jeor, and colleagues, based on indirect calorimetry of 498 healthy adults (251 women, 247 men) aged 19–78. It replaced the older Harris-Benedict equation (1919) as the preferred predictor of resting energy expenditure and was endorsed by the American Dietetic Association in 2005 as the most accurate of the common predictive equations. Limitations: it's a population-level estimate, not a personal one — it doesn't account for lean mass, ethnicity, metabolic adaptations from prolonged dieting, thyroid status, or medications. Use it as a starting point for calorie planning, then adjust based on real-world results over 2–4 weeks.