Calculate your Basal Metabolic Rate — the number of calories your body burns at rest. Also find your Total Daily Energy Expenditure (TDEE) based on activity level.
A BMR (Basal Metabolic Rate) Calculator estimates the minimum number of calories your body needs at complete rest just to maintain essential functions like breathing, circulating blood, cell repair, and regulating body temperature. This baseline figure forms the foundation for planning daily calorie needs for weight loss, maintenance, or muscle gain, since your total daily energy expenditure is essentially your BMR plus the extra calories burned through activity and digestion.
Most calculators use the Mifflin-St Jeor equation, considered more accurate than older formulas for most modern populations. For men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5. For women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161. Some versions also offer the older Harris-Benedict equation for comparison, though it tends to slightly overestimate calorie needs for many people compared to Mifflin-St Jeor.
Enter your gender, age, height, and current weight. The calculator returns your estimated BMR in calories per day, and often also shows your total daily energy expenditure (TDEE) once you select an activity level, which is the more practical number for setting a calorie target for weight management goals.
Example 1: A 30-year-old man who is 175 cm tall and weighs 75 kg has a BMR of (10×75) + (6.25×175) − (5×30) + 5 = 750 + 1093.75 − 150 + 5 ≈ 1,699 calories per day.
Example 2: A 28-year-old woman who is 162 cm tall and weighs 60 kg has a BMR of (10×60) + (6.25×162) − (5×28) − 161 = 600 + 1012.5 − 140 − 161 ≈ 1,312 calories per day.
What is the difference between BMR and TDEE? BMR is the calorie total needed at complete rest with no activity at all, while TDEE (Total Daily Energy Expenditure) adds in the calories burned through daily movement, exercise, and digestion, making TDEE the more relevant number for setting an actual daily calorie target.
Why does BMR decrease as you get older? Aging is generally associated with a gradual loss of lean muscle mass and a slight slowdown in cellular metabolic activity, both of which reduce the number of calories the body needs at rest, which is why the formula subtracts a factor based on age.
Does muscle mass affect BMR? Yes, muscle tissue burns more calories at rest than fat tissue does, so two people with the same weight but different body compositions can have meaningfully different BMR values, with the more muscular person typically burning more calories at rest.
How accurate are BMR formulas compared to lab testing? Formula-based estimates like Mifflin-St Jeor are reasonably accurate for most people, typically within about 10% of measured values from indirect calorimetry, though individual metabolic variation means lab testing remains the gold standard for anyone needing a precise figure.
Should I eat below my BMR to lose weight faster? Eating consistently below BMR is generally discouraged, since it can slow metabolism over time, increase muscle loss, and make sustainable weight loss harder; most nutrition guidance instead recommends a moderate calorie deficit below your TDEE rather than below your BMR.
Why do men typically have a higher BMR than women of the same weight? Men generally carry more lean muscle mass and less body fat than women at the same body weight, and since muscle is more metabolically active than fat tissue, this typically results in a higher resting calorie burn for men.
Can extreme dieting lower my BMR permanently? Prolonged very low-calorie dieting can trigger metabolic adaptation, where the body temporarily reduces its energy expenditure to conserve resources; this effect is usually reversible over time with adequate nutrition, though repeated extreme dieting cycles can make sustained weight management more difficult.
How often should I recalculate my BMR? It's worth recalculating whenever your weight changes significantly, roughly every 5–10% change in body weight, or every few months during an active weight loss or muscle-building program, since BMR shifts as body composition and weight change over time.
Why do the Mifflin-St Jeor and Harris-Benedict formulas give slightly different results? The Harris-Benedict equation was developed nearly a century earlier using a smaller, less diverse study population, while Mifflin-St Jeor was recalibrated using more modern data and is now generally considered more accurate for the average person, which is why most calculators default to it.
Does genetics play a role in BMR differences between individuals? Yes, genetic factors influencing thyroid function, muscle fiber composition, and overall metabolic efficiency mean that two people with identical height, weight, and age can still have a somewhat different true BMR, even though formulas can only estimate based on the measurable inputs available.
Does climate or season affect BMR? Some research suggests BMR can shift slightly with seasonal temperature changes, as the body adjusts to maintain core temperature, though this effect is generally small compared with the impact of body weight, muscle mass, and age on overall resting energy expenditure.