Basal Metabolic Rate (BMR): The Foundation of Your Calorie Budget

Basal Metabolic Rate is the number of calories your body burns at complete rest over 24 hours — just to keep your heart beating, lungs breathing, and organs running. It accounts for 60–75% of most people's total daily calorie burn, making it the most important single factor in any nutrition plan.

The two main formulas

The Harris-Benedict formula (1919) was the standard for decades but has been shown to overestimate BMR slightly. The Mifflin-St Jeor formula (1990) is now considered more accurate for most adults and is the default in our calculator. Both formulas use age, height, weight, and sex as inputs.

What raises and lowers BMR

Muscle tissue burns more calories at rest than fat tissue, so more muscle mass raises BMR. Age decreases BMR by roughly 1–2% per decade after 20. Fever temporarily raises it. Crash dieting can lower it significantly — one reason why very low calorie diets often fail over the long term.

BMR vs. TDEE

BMR is your resting baseline. Your Total Daily Energy Expenditure (TDEE) is BMR multiplied by an activity factor. Most people confuse the two and mistakenly eat at their BMR — which is much lower than what they actually burn. Enter your details into the BMR calculator to see your true resting baseline, then check the calorie/TDEE calculator for your real daily target.