BMR Calculator
Basal Metabolic Rate — calories burned at complete rest. Results shown for both Mifflin-St Jeor and Harris-Benedict formulas.
What is BMR?
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to sustain basic life functions at complete rest — breathing, circulation, temperature regulation, and cell production. Think of it as the energy cost of simply being alive.
BMR typically accounts for 60–75% of total daily calorie expenditure. The remainder comes from physical activity and digesting food. Muscle mass is the largest driver of BMR — the more lean muscle you have, the higher your resting metabolism.
We show two formulas: Mifflin-St Jeor (1990) is considered more accurate for modern populations; Harris-Benedict (revised 1984) has been used longer and may be more familiar to clinicians.
BMR calculator — FAQ
Yes — the most effective way to raise BMR is to build lean muscle mass through resistance training. Muscle tissue burns more calories at rest than fat tissue. Eating adequate protein (0.8–1g per lb of bodyweight), staying hydrated, getting sufficient sleep, and avoiding prolonged severe caloric restriction all help maintain a healthy metabolic rate.
Yes, BMR tends to decline with age — primarily because most people lose muscle mass as they age (a process called sarcopenia). The decline is roughly 1–2% per decade after age 30. However, maintaining muscle through strength training can significantly offset this decline. Age-related metabolic slowdown is largely a loss of muscle story, not an inevitable fate.
They use slightly different coefficients derived from different study populations. The Harris-Benedict equation was developed in 1919 (revised in 1984) and tends to overestimate BMR by 5% on average. The Mifflin-St Jeor equation was published in 1990 using a larger, more diverse population and is now recommended by most dietetic associations as the more accurate formula.