BMR Calculator

Understanding your Basal Metabolic Rate

Your Basal Metabolic Rate is the number of calories your body needs just to stay alive: breathing, circulating blood, repairing cells, and keeping your brain running, all while lying still for 24 hours. It typically makes up 60-75% of total daily calorie burn for most people, which is why understanding it matters more than many realize when planning a diet.

This calculator uses the Mifflin-St Jeor equation, published in 1990 and validated repeatedly since as one of the more accurate predictive formulas for the general population, especially compared to the older Harris-Benedict equation from 1919. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. The five-point gap between the male and female constants reflects average differences in muscle mass and body composition, since muscle tissue burns more calories at rest than fat tissue.

BMR is not the same as the calories you should eat — it's the floor, not the target. Consistently eating below your BMR for extended periods can signal your body to conserve energy, slow metabolism, and break down muscle rather than fat. That's why this page also shows your estimated needs at five different activity levels: multiplying BMR by an activity factor gives your Total Daily Energy Expenditure (TDEE), a far more useful number for everyday planning. Factors like extreme calorie restriction, certain medications, thyroid conditions, and significant muscle loss with age can all lower real-world BMR below what any formula predicts, so treat this as a solid starting estimate rather than a lab-measured value.

Frequently asked questions

Is BMR the same as the calories I should eat? No — BMR is only what your body burns at complete rest. Add activity on top of it (or use the calorie calculator, which does this automatically) to get a realistic daily target.

Why does BMR drop as people age? Muscle mass tends to decline with age unless it's actively maintained through resistance training, and muscle burns more energy at rest than fat tissue, so BMR falls along with it.

Can two people with the same height and weight have different BMRs? Yes. Body composition, genetics, thyroid function, and muscle mass all shift BMR even when the numbers on a scale match, which is exactly why the formula is an estimate rather than a lab measurement.

Worked example

A 40-year-old man, 178 cm, 82 kg: BMR = 10(82) + 6.25(178) − 5(40) + 5 = 1737.5 kcal/day. That’s the energy his body burns at total rest — before any activity is added on top.

Is BMR the same as the number I should eat? No — BMR is only the resting baseline. You still need to add calories for daily movement and exercise (that's what the Calorie Calculator's activity multiplier does) before you get a realistic daily target.

Why do two calculators sometimes give slightly different BMR numbers? Different formulas (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle) weigh age, height, and lean mass differently. Mifflin-St Jeor, used here, is generally considered the most accurate for the general population today.