BMR Calculator

Your basal metabolic rate (BMR) is the number of calories your body burns at complete rest just to stay alive: keeping your heart beating, your lungs working, your temperature steady and your cells repairing. For most people it is the single largest part of daily energy use, which is why it is the starting point for any calorie or weight plan.

This calculator estimates BMR with the three equations used in practice. The Mifflin-St Jeor equation (1990) is the one most dietary guidelines now recommend for healthy adults. The revised Harris-Benedict equation (1984) is the long-standing classic. The Katch-McArdle equation uses your lean body mass instead of height and age, so it can be more accurate if you are lean or muscular and know your body fat percentage.

It shows all three side by side so you can see how much they agree. Differences of 100 to 200 kcal between formulas are normal, because each was derived from a different group of people and uses slightly different inputs.

From your BMR the tool derives your total daily energy expenditure (TDEE) by applying an activity factor, from sedentary up to very active. TDEE is the more useful number day to day, because it reflects how much you actually burn once movement and exercise are included, and it is what you compare against how much you eat. BMR is only the resting part.

BMR estimates have real limits. Metabolism varies between people of the same size because of genetics, hormones, body composition and health, so two people with identical stats can differ by hundreds of calories. Treat the result as a well-informed starting point, then adjust based on how your weight actually responds over a few weeks.

The equations were built for average healthy adults, so they are least reliable at the extremes: very muscular or very lean bodies, older adults, and people with thyroid or other metabolic conditions. They are not designed for children, teenagers or pregnancy, which need age- and situation-specific references. If any of these apply, use the number cautiously and ask a professional.

Use your BMR and TDEE as a baseline. To turn them into a calorie target with weight-goal adjustments and a macro split, use the calorie calculator. To feed the Katch-McArdle formula with your body composition, use the body fat calculator. Everything is worked out in your browser, and you can switch between metric and imperial units at any time.