BMR Calculator: Basal Metabolic Rate
Your BMR — basal metabolic rate — is the number of calories your body burns at complete rest just to stay alive: breathing, heartbeat, brain function and cell repair. It is the single biggest slice of your daily calorie burn, usually 60 to 75% of the total. This free BMR calculator uses the Mifflin-St Jeor equation, the formula preferred by dietitians and sports scientists, to estimate yours in seconds.
BMR Calculator
How to Use This BMR Calculator
Start by picking the unit system you use every day — metric (kilograms and centimeters) or imperial (pounds, feet and inches) — and enter your sex and age. Age matters because the equation accounts for the slow metabolic decline that begins in your twenties, and sex matters because men and women have different formulas.
Enter your current weight and height and click Calculate. You will see your BMR in calories per day, along with a summary of the numbers used. If you are unsure of your height, stand against a wall, mark the top of your head and measure with a tape measure — do not round from memory.
Your BMR is not the number of calories you should eat — it is the floor, the resting burn. To turn it into a real daily calorie target, multiply it by an activity factor (1.2 to 1.9) using our TDEE Calculator.
The Formula
This calculator uses the Mifflin-St Jeor equation, published in 1990 and now the most widely recommended predictive formula:
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Worked example: a 30-year-old man who weighs 70 kg and is 170 cm tall has a BMR of 10 × 70 + 6.25 × 170 − 5 × 30 + 5 = 700 + 1062.5 − 150 + 5 = 1617.5 — about 1,618 calories per day. A woman of the same age, weight and height scores 166 lower: 1,451.5, about 1,452 calories per day. The 166-point gap is the difference between the +5 and −161 adjustments in the two formulas.
Tips for Using Your BMR
Weigh yourself first thing in the morning, after using the bathroom and before eating, and use the same scale every time. Weighing at different times of day can shift your number by a couple of pounds and make your BMR look higher or lower than it really is.
Recalculate your BMR after a weight change of about 10 lb (5 kg) or any big shift in muscle mass. The equation depends on your current weight — a 20 lb drop lowers your BMR by roughly 90 calories per day, which matters for your calorie plan.
Your BMR is a number, not a verdict. Build muscle with resistance training and hit your protein targets and your resting burn goes up — muscle tissue burns noticeably more calories than fat, even while you sleep.
Frequently Asked Questions
What is BMR and why does it matter?
BMR (basal metabolic rate) is the number of calories your body burns at complete rest just to stay alive — breathing, heartbeat, brain function, cell repair and temperature control. It makes up about 60 to 75% of your total daily burn, so it is the baseline every calorie plan is built on.
What's the difference between BMR and TDEE?
BMR is the resting burn only. TDEE (total daily energy expenditure) adds everything else — work, walking, workouts and digestion — and is usually 1.2 to 1.9 times higher than your BMR depending on how active you are. You lose weight by eating below your TDEE, not below your BMR.
How accurate is the Mifflin-St Jeor equation?
It is the most accurate general-purpose formula and predicts BMR within about 10% for most people. It tends to underestimate the burn of very muscular people and overestimate for very overweight people, because it uses total weight rather than lean mass.
How can I increase my BMR?
The practical levers are muscle mass and body size. Adding muscle with resistance training raises your resting burn, and keeping your protein intake around 1.2–2.2 g per kg of body weight helps preserve muscle when you diet. Short-term boosts from eating and exercise are small — the real gains come from body composition.
Why does BMR drop as you age?
Muscle mass declines by roughly 3 to 8% per decade after age 30 if it is not trained, and muscle is metabolically active tissue. Hormone changes and a less active daily life compound the effect. That is why the Mifflin-St Jeor equation subtracts 5 calories per year of age — and why strength training is one of the best investments you can make in your metabolism.