BMR calculator

Your basal metabolic rate (BMR) is the number of calories your body burns at complete rest to run its most basic functions — breathing, circulating blood, keeping your body temperature steady, and repairing cells. It's the energy you'd use if you stayed in bed all day and didn't move.

BMR typically accounts for the largest share of the calories you burn each day, often around 60–70% for most people. Because it's the biggest single piece of your daily energy use, it's a useful starting point for understanding how food and activity fit together.

BMR is an estimate, not a measured value. It's shaped by your size, age, sex, muscle mass, genetics, and other factors. Two people with the same height and weight can still have different real-world metabolisms, so treat the number as a well-grounded ballpark rather than a precise readout.

This tool uses the Mifflin-St Jeor equation, first published in 1990 and now widely considered one of the most accurate BMR formulas for the general population. It takes your weight in kilograms, height in centimeters, and age in years, then adjusts by sex. (We convert your pounds, feet, and inches for you.)

For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5.

For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161.

The two formulas are identical except for the final constant, which reflects average differences in body composition. Older equations like Harris-Benedict often give slightly higher estimates; Mifflin-St Jeor tends to track more closely to measured resting metabolism for most adults.

You'll often see BMR used interchangeably with RMR (resting metabolic rate), but they aren't quite the same. BMR is measured under strict laboratory conditions — after an overnight fast, fully rested, and lying still in a temperature-controlled room. RMR is measured under less rigid conditions and usually comes out slightly higher.

The difference is small — often just a few percent — so for everyday planning the terms are close enough to treat as the same idea. The Mifflin-St Jeor equation is commonly used to estimate both.

Think of your BMR as the floor: the minimum energy your body needs before you factor in any movement. On its own it doesn't tell you how many calories to eat, because it doesn't include the calories you burn walking, working, exercising, or even digesting food.

To turn BMR into a daily calorie target, you multiply it by an activity factor to estimate your total daily energy expenditure (TDEE) — the full picture of what you burn in a day. From there, a modest calorie deficit below your TDEE is what supports gradual weight loss. Our TDEE calculator and calorie-deficit calculator build on the same BMR shown here.

Eating far below your BMR for long stretches isn't a good strategy — it can be hard to sustain and may not give your body the fuel it needs. Aggressive or very-low-calorie plans should only be done under the guidance of a licensed healthcare provider.