BMR Calculator
Enter your details — your BMR updates as you type. This is a general estimate, not a medical measurement, and it isn't medical advice.
How this calculator works
This tool estimates BMR using the Mifflin-St Jeor equation, published in 1990 and now the modern standard used by dietitians and clinicians — validation studies comparing it against measured resting metabolic rate have generally found it more accurate than the older Harris-Benedict formula from 1919 (revised 1984). For men, BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women, BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. The result is a general estimate, not a medical measurement — see the FAQ below for its real limitations.
Worked example
A 30-year-old male weighing 80 kg at 180 cm tall: BMR = (10 × 80) + (6.25 × 180) − (5 × 30) + 5 = 800 + 1125 − 150 + 5 = 1,780 calories per day. That's the energy his body needs before he takes a single step — to find out what he needs including activity, the next stop is the calorie calculator.
Frequently asked questions
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body burns in 24 hours doing absolutely nothing — no walking, no digesting a meal, not even sitting up. It's the energy your organs, brain, and cells need just to keep you alive at complete rest. Every calorie you burn on top of BMR comes from movement, exercise, and digesting food.
Why does the Mifflin-St Jeor equation replace the older Harris-Benedict formula?
Harris-Benedict dates to 1919 and was revised in 1984, but body composition and lifestyles have shifted a lot since then. When researchers compared both formulas against measured metabolic rate in validation studies, Mifflin-St Jeor (published in 1990) consistently came out more accurate for most adults, which is why it's now the equation dietitians and clinicians default to.
Does muscle mass affect my BMR?
Yes, meaningfully — muscle tissue burns more calories at rest than fat tissue, so two people with the same weight, height, sex, and age can have genuinely different metabolic rates depending on body composition. This is a real limitation of the Mifflin-St Jeor equation: it works from weight, height, age, and sex only and doesn't measure how much of that weight is muscle versus fat. If you know your body fat percentage, a lean-mass-based formula will usually get closer to your true number.
What do I do with my BMR number?
BMR by itself isn't a calorie target — it's the floor, not the number to eat. To find out how many calories you actually need in a day, add back the energy you burn from movement and exercise. That's exactly what our calorie calculator does: it takes the same inputs, applies an activity multiplier, and gives you a maintenance calorie number you can actually use for a diet or fitness goal.
Is this a medical recommendation?
No. This calculator produces a general estimate from a population-average formula — it is not a medical or clinical measurement of your individual metabolism, and it isn't medical advice. Actual metabolic rate varies with genetics, health conditions, medications, and other factors this equation can't see. If you have a medical condition or specific health goal, talk to a doctor or registered dietitian before making decisions based on this number.