BMR Calculator

Your basal metabolic rate is the quiet baseline underneath every diet conversation: the number of calories your body burns in a full day of doing absolutely nothing. Not sleeping, exactly, and not lying motionless in a lab — but at complete physical and digestive rest, so the figure captures only the energy your organs spend staying alive. Your brain, heart, kidneys, and liver do the heavy lifting here; keeping them running, holding your body temperature steady, and repairing cells accounts for the overwhelming majority of BMR. Because it is measured at rest, BMR deliberately excludes every calorie you burn through movement, from a workout down to fidgeting in a chair. That distinction is the whole reason the number matters: it tells you the floor your intake should not normally drop below, and it is the anchor that activity multipliers are built on top of. Two people who weigh the same can land hundreds of calories apart on this number, which is why guessing from weight alone so often goes wrong.

Older textbooks lean on the Harris-Benedict formula from 1919, while most modern guidance prefers Mifflin-St Jeor, published in 1990. The two are not interchangeable: Harris-Benedict was built from a small sample of mostly younger, leaner people and tends to overestimate modern, less active populations, sometimes by a few hundred calories a day. Mifflin-St Jeor was derived against a broader group and lines up better with how people actually burn energy today, which is why it is the default headline figure on this page and the one most dietitians reach for. Showing both side by side is not padding — it lets you see how far the estimates diverge for your specific body, and the "Difference" row tells you the gap at a glance. If the two are close, you can plan with confidence; if they are far apart, treat the range as a reminder that any equation is an estimate, not a meter reading. Use Mifflin-St Jeor as your working number and keep Harris-Benedict as the cross-check. BMR on its own is too low to live on, because it assumes you never move. To get a realistic daily number you multiply BMR by an activity factor — roughly 1.2 for a sedentary life, up through 1.55 for moderate exercise a few days a week, to 1.725 or higher for a physically demanding routine. The result is your total daily energy expenditure, or TDEE, and it is the figure you should actually budget around. From there the math is straightforward: eat about 500 calories a day below TDEE to lose roughly a pound a week, or 500 above to gain. Because BMR sits underneath TDEE, a small error in your BMR propagates into the target, which is exactly why estimating it honestly — with real height, weight, age, and sex — beats rounding. If you want the full activity-factor walkthrough rather than a single estimate, the calorie calculator on this site carries the multiplication through to finished numbers. A BMR estimate is a starting point, not a verdict. It assumes an average body composition for your stats, so someone with above-average muscle or a medical condition that shifts metabolism will sit off the formula's line in either direction. It also says nothing about the quality of the calories you eat — 1,500 calories of vegetables and protein and 1,500 calories of refined sugar move your weight the same way but leave your body in very different states. Treat the number as a floor to stay above for health and a base to build a target on, then adjust from real results: if your weight drifts contrary to plan for a few weeks, nudge intake rather than distrusting the calculator entirely. Re-run it whenever your body changes substantially, since the inputs that drive the equation shift with you. Used this way, BMR becomes a reliable anchor for everyday food decisions instead of a single number you check once and forget.

BMR is one input in a larger picture, and keeping it in context stops it being misunderstood. It is not your weight-loss target, your maintenance calories, or the number a fitness tracker reports at the end of the day — those are TDEE, adjusted for your real movement, which is almost always several hundred calories higher than BMR. It is also not a body-composition score: two people with identical BMR can look and feel completely different if one carries more muscle and the other more fat, because the equation only sees age, sex, height, and weight. For that reason, pairing a BMR estimate with a body-fat reading gives a sharper view of your metabolism than either alone, since more lean mass quietly raises the floor. When comparing calculators on this site, think of BMR as the foundation the calorie calculator builds on, and body-fat as the context that explains why that foundation looks the way it does for your particular frame.