Free Tool · Nutrition
BMR Calculator
Calculate your Basal Metabolic Rate using the Mifflin-St Jeor equation. This is the number of calories your body burns keeping you alive at complete rest, before a single step of activity.
How it works
The math behind your metabolism
The Mifflin-St Jeor equation is a regression formula derived from measured resting metabolic rates in hundreds of adults. It takes four inputs: body weight in kilograms, height in centimeters, age in years, and biological sex. The output is the calories your body needs per day before any movement.
For men: BMR = 10 × weight + 6.25 × height - 5 × age + 5. For women, subtract 161 at the end instead of adding 5. The 161-calorie gap reflects average differences in body composition between men and women of the same height and weight.
BMR makes up the largest single slice of your daily calorie burn for anyone not working a physically demanding job. It is the floor you build every nutrition plan on top of.
Frequently asked questions
Questions we hear a lot
Basal Metabolic Rate is the number of calories your body needs to keep essential functions running at complete rest: heart, brain, kidneys, liver, lungs, body temperature. It accounts for roughly 60 to 75 percent of your total daily calorie burn for most sedentary adults.
The Mifflin-St Jeor equation, published in 1990 and widely considered the most accurate predictive formula for healthy adults. It improved on the older Harris-Benedict equation by roughly 5 percent on average. The Academy of Nutrition and Dietetics recommends Mifflin-St Jeor as the default.
Predictive formulas like Mifflin-St Jeor estimate BMR within about 10 percent of a measured value for most people. Individual variation from genetics, muscle mass, thyroid function, and other factors can shift the true number. Use the output as a starting point and recalibrate based on 2 to 4 weeks of real-world results.
Resting Metabolic Rate (RMR) is measured after a short rest but without the strict overnight fast required for true BMR. The two are within a few percent of each other in practice, and most consumer calculators use the terms interchangeably.
Yes. BMR declines roughly 1 to 2 percent per decade in adulthood, largely because lean muscle mass drops if untrained. Staying active and lifting regularly preserves more BMR than cardio alone.
BMR on its own is only part of the picture. Multiply by an activity factor to get TDEE (Total Daily Energy Expenditure), then create a deficit or surplus from there. Use our TDEE calculator to go straight to the full picture.