BMR Calculator

How this is calculated

BMR = 10×kg + 6.25×cm − 5×age + (male: +5 · female: −161)

Worked example: male, 30, 80 kg, 180 cm → 800 + 1,125 − 150 + 5 = 1,780 kcal/day — about 74 kcal every hour, awake or asleep. To turn BMR into a daily eating target, multiply by an activity factor on the TDEE calculator; eating at BMR itself is a heavy deficit, not maintenance. Estimates, not medical advice.

The four equations, and why we use Mifflin–St Jeor

Several formulas estimate resting energy expenditure, and they do not agree. Harris–Benedict, published in 1919 and revised in 1984, is the oldest in common use and tends to run a little high for modern bodies. Mifflin–St Jeor, published in 1990, was derived from a larger and more representative sample and is the one the Academy of Nutrition and Dietetics recommends for healthy adults; it predicts measured resting rate within about 10% for roughly seven people in ten. Katch–McArdle takes a different route, working from lean body mass rather than total weight, which makes it the most accurate of the set for people who know their body-fat percentage and the least usable for everyone else.

This page uses Mifflin–St Jeor because it needs only height, weight, age and sex, and is the best-validated formula that asks for nothing you would have to measure in a laboratory. It is worth knowing that the "10%" accuracy is a population statistic: for any individual, the true figure can sit several hundred calories away from the estimate, and nothing in the arithmetic can tell you whether you are one of those people.

What basal rate actually covers

Basal metabolic rate is the energy your body spends doing nothing — lying still, awake, in a comfortable room, having not eaten for twelve hours. It is not a small residue. For most sedentary adults it accounts for 60–70% of total daily energy use, which surprises people who assume exercise dominates. The brain alone takes roughly a fifth of it, the liver and kidneys a similar share, and the heart never stops. This is why a large person burns more than a small one even at rest: there is more tissue to keep running.

Activity multipliers are the weak link

Turning basal rate into daily energy use means multiplying by an activity factor, and that is where the real uncertainty lives. The standard bands — sedentary 1.2, lightly active 1.375, moderately active 1.55, very active 1.725, extremely active 1.9 — are coarse, self-reported, and systematically over-estimated by most people. The gap between 1.375 and 1.55 on a 1,600-calorie basal rate is 280 calories a day, which is more than the entire difference most people are trying to create when they change how they eat.

Two practical corrections. First, a desk job with three gym sessions a week is usually "lightly active", not "moderately active" — an hour of exercise does not offset twenty-three hours of sitting as much as people expect. Second, non-exercise movement matters more than the labels suggest: fidgeting, standing, walking to shops and taking stairs can vary by hundreds of calories a day between two people with identical formal exercise, and it tends to fall quietly when you eat less.

Treat the number as a hypothesis to test

The reliable way to use this estimate is as a starting point you then correct with evidence. Eat at the figure for two to three weeks, weighing yourself under consistent conditions — same time of day, same circumstances, and preferably averaging seven days rather than reading any single morning, because water shifts of a kilogram or more are routine and mean nothing. If weight is stable, you have found your actual maintenance intake, which is worth far more than any equation. If it moved, adjust by 100–200 calories and repeat.

Expect the target to move as you do. Losing weight lowers basal rate simply because there is less tissue, and metabolic adaptation lowers it a little further, so the intake that produced steady loss in month one often produces a plateau by month four. That is normal physiology rather than a failure of will.

When an equation is the wrong tool

Mifflin–St Jeor was derived from healthy adults, and it degrades outside that group. Thyroid disorders move resting rate substantially in both directions. Considerable muscle or considerable obesity both push the estimate off, in opposite directions, because the formula uses total weight rather than composition. Pregnancy, breastfeeding, growth, serious illness and recovery from surgery all change requirements in ways no height-and-weight formula captures. If you are being treated for anything that touches metabolism or eating, work from measured values with a clinician rather than from this page.