What is BMR?
Your basal metabolic rate is the amount of energy your body needs to keep its basic functions going while you are completely at rest – breathing, pumping blood, maintaining body temperature and repairing cells. For most people it accounts for 60–70% of the calories they burn each day. Knowing your BMR is the first step in planning a diet, because every other estimate of energy needs is built on top of it.
How to use this BMR calculator
Enter your age, sex, height and weight in metric or US units. The main result uses the Mifflin-St Jeor equation. For comparison you'll also see the revised Harris-Benedict equation, an older formula that tends to give slightly higher numbers. If you know your body-fat percentage, enter it to get the Katch-McArdle estimate, which is based on lean body mass and is often more accurate for lean or very muscular people. The table then multiplies your BMR by standard activity factors to show daily calorie needs from sedentary to very active.
The formulas
Mifflin-St Jeor (women): 10W + 6.25H − 5A − 161
Katch-McArdle: 370 + 21.6 × lean mass (kg)
W is weight in kilograms, H is height in centimeters and A is age in years.
What affects your BMR?
- Muscle mass: muscle burns more energy at rest than fat, so strength training can raise BMR.
- Age: BMR typically declines with age, largely due to loss of muscle.
- Body size: larger bodies need more energy to maintain.
- Sex: men usually have higher BMR because of greater average muscle mass.
- Hormones and health: thyroid function, illness and some medications change metabolic rate.
BMR from an equation is an estimate. A laboratory test using indirect calorimetry is the only way to measure it precisely.
Frequently asked questions
What is the difference between BMR and RMR?
BMR is measured under strict lab conditions after fasting and full rest; RMR (resting metabolic rate) is measured under looser conditions and is usually slightly higher. In practice the two are used interchangeably.
Which BMR formula is most accurate?
For the general population Mifflin-St Jeor is usually the most accurate. If you know your body fat percentage, Katch-McArdle can be better for lean, muscular people.
Should I eat only my BMR in calories?
No. BMR excludes all activity. Eating at or below BMR for long periods is usually too low; use your TDEE as the baseline.
How can I increase my BMR?
Building muscle through resistance training, staying active and eating enough protein help maintain or raise your metabolic rate.
Last reviewed 2026-10-27. This bmr calculator is provided for general information; verify important decisions with a qualified professional.