Free BMR calculator. Find your basal metabolic rate using the Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle formula.
A BMR calculator estimates the number of calories your body burns at complete rest just to keep vital functions running, using your weight, height, age, and gender (or lean body mass, if you know your body fat percentage) in a validated formula.
1699 kcal/day
Your BMR
Last updated:
BMR Calculator
Basal Metabolic Rate is the amount of energy your body needs just to stay alive at complete rest — no movement, no digestion, no exercise. It powers your heartbeat, breathing, brain activity, and the constant repair and replacement of cells throughout your body. For most people, BMR accounts for the majority of the calories they burn in a day, even before they get out of bed.
Because BMR is a baseline rather than a fixed number, it's estimated using equations built from population data on weight, height, age, and gender. These formulas aren't a substitute for a lab measurement (indirect calorimetry), but they're accurate enough for practical calorie planning, which is why they're the standard tool used by dietitians and fitness professionals.
Choosing a Formula
The Harris-Benedict equation, first published in 1919 and revised in 1984, was for decades the default BMR formula. Research since then has shown it tends to overestimate BMR for many people, particularly those who are overweight, because it was derived from a study population that doesn't reflect today's broader range of body types.
Mifflin-St Jeor, published in 1990, was developed specifically to correct this and has consistently shown better accuracy in validation studies against measured BMR, which is why it has replaced Harris-Benedict as the standard in most clinical and fitness settings. Katch-McArdle takes a different approach entirely: instead of using total body weight, it calculates BMR from lean body mass alone, which makes it the most precise choice for anyone who knows their body fat percentage — particularly athletes and bodybuilders, where fat and muscle ratios vary widely between people of the same weight.
From BMR to Daily Needs
BMR only tells you what your body burns lying completely still — it excludes the energy cost of digestion, daily movement, and any deliberate exercise. To get a realistic daily calorie number, BMR needs to be multiplied by an activity multiplier, ranging from around 1.2 for a mostly sedentary lifestyle up to 1.9 or higher for very physically demanding jobs or intense training schedules. This adjusted figure is what's known as TDEE, or Total Daily Energy Expenditure.
Using BMR directly as a calorie target — rather than as an input to a larger calculation — is one of the most common mistakes in calorie planning, since it would represent a severe deficit for almost anyone who isn't bedridden, and sustained eating at that level typically triggers muscle loss and a metabolic slowdown rather than healthy fat loss.
Practical Considerations
All BMR formulas are population averages, so any individual's actual metabolic rate can differ by 10% or more from the estimate due to genetics, muscle mass, hormonal factors (including thyroid function), and even how consistently someone has dieted in the past. The estimate is a well-informed starting point, not a fixed diagnosis — it's meant to be adjusted based on real-world results over a few weeks.
Body fat percentage, when used with the Katch-McArdle formula, is itself an estimate in most cases (from calipers, bioelectrical impedance scales, or visual estimation), so its accuracy directly affects the BMR result. If you don't have a reasonably reliable body fat measurement, Mifflin-St Jeor using total body weight will generally give a more dependable estimate than Katch-McArdle with a rough guess.
Practical Use Cases
Setting a calorie deficit or surplus
Use BMR as the starting point before applying an activity multiplier to find your maintenance calories.
Comparing formula results
Check how Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle estimates differ for your body.
Tracking metabolic changes over time
Recalculate BMR as your weight or body composition changes during a fitness program.
Planning nutrition with known body fat percentage
Use the Katch-McArdle formula for a lean-mass-based estimate if you track body fat.
Understanding age-related metabolic decline
See how BMR estimates shift as age increases at the same weight and height.
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to keep essential functions running — breathing, circulation, cell production, and organ function. It typically makes up 60-75% of your total daily calorie burn, so it's the foundation for setting any calorie target, whether for weight loss, maintenance, or muscle gain.
Mifflin-St Jeor is generally considered the most accurate for the general population and has been the standard used by dietitians since the mid-2000s. Harris-Benedict is an older formula that tends to slightly overestimate BMR. Katch-McArdle is the most precise option if you know your body fat percentage, since it calculates BMR from lean body mass rather than total weight — which matters more for very lean or very muscular people.
No. BMR only reflects calories burned at complete rest — it doesn't include the energy used for walking, exercising, digesting food, or daily activity. To find your actual daily calorie needs, BMR is multiplied by an activity factor (this is called TDEE, or Total Daily Energy Expenditure). Eating exactly at your BMR would only be appropriate if you spent the entire day lying still.
BMR declines with age mainly because of a gradual loss of muscle mass, which is more metabolically active than fat tissue. Hormonal changes also play a role. This is reflected directly in the Mifflin-St Jeor and Harris-Benedict formulas, both of which subtract a factor based on age — meaning two people of the same weight and height will get a lower BMR estimate the older they are.
Yes, to some degree. Building muscle through resistance training is the most reliable way to raise BMR long-term, since muscle tissue burns more calories at rest than fat tissue. Adequate sleep and avoiding very low-calorie crash diets also help preserve BMR — severe calorie restriction can cause your body to lower its metabolic rate as an adaptive response.