Basal metabolic rate is the energy your body needs for its non-negotiable jobs: breathing, circulating blood, regulating temperature, growing cells. It accounts for roughly 60–70% of most people's daily calorie burn, which makes it the foundation every diet plan is built on.
Enter your sex, age, height and weight and the calculator applies the Mifflin-St Jeor equation — the formula researchers find most accurate for typical adults. The result is a daily calorie floor: eat far below it for long and your body starts economizing, slowing you down and making diets backfire.
Part of the Health Calculators collection on CountCrunch.
The BMR formula
A 40-year-old man at 180 cm and 80 kg: 10 × 80 + 6.25 × 180 − 5 × 40 + 5 = 1,730 kcal/day at rest. Everything he does beyond lying still adds on top.
What raises or lowers your BMR
- Muscle mass is the biggest lever you control — muscle burns more at rest than fat does, which is why strength training helps long-term weight control.
- Age: BMR drifts down about 1–2% per decade after 40, mostly as muscle is lost.
- Body size: taller, heavier bodies cost more energy to run.
- Crash dieting can suppress BMR temporarily as the body adapts to low intake.
How to use your BMR
BMR alone is not an eating target — almost nobody lies still all day. Multiply it by your activity level to get TDEE, your real daily burn, and plan meals from there. Think of BMR as the floor your intake should rarely drop beneath.
Frequently asked questions
What is a normal BMR?
Most adults land between roughly 1,200 and 2,000 kcal/day at rest, depending on size, sex, age and muscle mass. Smaller, older women trend lower; larger, younger, muscular men trend higher.
Should I eat below my BMR to lose weight?
Not as a routine. Eating below BMR for extended periods can increase hunger hormones, cost muscle and slow your metabolism. A moderate deficit from your TDEE is safer and more sustainable.
Does building muscle really raise BMR?
Yes, modestly. Muscle burns roughly 6 kcal per pound per day at rest versus about 2 for fat. Gaining several kilos of muscle adds a meaningful, permanent bump to daily burn.
How is BMR different from RMR?
BMR is measured under strict lab conditions (fasted, rested, thermally neutral). RMR (resting metabolic rate) is measured more casually and runs about 10% higher. For planning purposes they are used interchangeably.