BMR Calculator

Basal Metabolic Rate (BMR) is the number of calories your body needs each day just to keep itself running — breathing, circulating blood, repairing cells, and maintaining body temperature — with no movement or digestion included. It's the energy cost of simply being alive, measured at complete rest.

This calculator uses the Mifflin-St Jeor equation, developed by Mifflin and St Jeor in 1990 and now the formula recommended by the Academy of Nutrition and Dietetics for most adults, having replaced the older Harris-Benedict equation from 1919. It calculates BMR from your weight, height, age, and sex, since sex affects the equation because men typically carry more lean muscle mass than women at the same weight and height, and muscle tissue burns more calories at rest than fat tissue does.

Your BMR is a starting point, not your full calorie need. To find out how many calories you actually burn in a day, BMR gets multiplied by an activity factor that accounts for exercise, daily movement, and the energy your body spends digesting food — that total is called Total Daily Energy Expenditure (TDEE). Like any predictive formula, Mifflin-St Jeor gives a population-average estimate; individual factors like genetics, muscle mass, and hormone levels can shift your real BMR up or down from what's shown here.

A worked example

Take a 30-year-old woman who weighs 65 kg and is 165 cm tall. The shared part of the formula first: 10 × 65 = 650, plus 6.25 × 165 = 1,031.25, minus 5 × 30 = 150. That's 650 + 1,031.25 − 150 = 1,531.25. For women, the equation subtracts 161: 1,531.25 − 161 = 1,370.25, which rounds to a BMR of about 1,370 calories a day. For a man with the same weight, height, and age, the equation adds 5 instead: 1,531.25 + 5 = 1,536.25, rounding to 1,536 — about 166 calories higher, the entire size of the male/female difference in this formula.

Common mistakes when using your BMR

The biggest one is eating at or near your BMR number expecting fast weight loss. BMR only covers the energy your body needs lying still and unconscious — it doesn't include a single calorie for walking, working, digesting food, or exercising, so eating that little while living a normal day creates a much larger deficit than intended and isn't a sustainable target. BMR is also sometimes confused with RMR (Resting Metabolic Rate), a closely related but slightly higher number usually measured while awake that includes a small amount of digestion and arousal cost; the two get used interchangeably in everyday conversation, but they're measured under different conditions.

When the equation is less reliable

Mifflin-St Jeor was built from a sample of 498 people spanning normal-weight and obese adults, and clinical comparisons against measured resting metabolic rate have found it predicts within ±10% for about 82% of subjects — noticeably better than the older Harris-Benedict equation's roughly 68% — which is why the Academy of Nutrition and Dietetics recommends it as the default choice absent direct measurement. Still, "most people" isn't "everyone": prediction-equation studies consistently show lower accuracy in people with obesity than in people of average weight, and very muscular individuals can be underestimated too, since the formula only sees total weight and can't tell how much of it is lean muscle, which burns more at rest than fat tissue.

Turning BMR into a daily calorie plan

BMR by itself isn't a number to eat to — it's the foundation TDEE (Total Daily Energy Expenditure) is built on. TDEE multiplies BMR by an activity factor that accounts for movement, exercise, and digestion, and that larger number is what actually reflects how many calories you burn — and should generally aim to eat — across a full day. Use this BMR result as an input to a TDEE or calorie calculation, not as a daily target on its own.

Mifflin-St Jeor vs. Harris-Benedict

Harris-Benedict dates to 1919, built from calorimetry on 239 subjects, and was revised once in 1984; it tends to run higher than modern equations for today's average body composition. Mifflin-St Jeor, published seven decades later in 1990 on a larger and more representative sample, replaced it as the preferred formula for healthy adults. Both estimate the same underlying quantity from similar inputs, but Mifflin-St Jeor's better fit to modern populations is why it's the formula this calculator — and most current clinical nutrition guidance — uses by default.