Free BMR Calculator – Calculate Basal Metabolic Rate

What Is BMR and How the BMR Calculator Works

Basal Metabolic Rate is the number of calories your body spends staying alive while doing nothing at all. Breathing, pumping blood, holding your temperature steady, repairing cells, running your brain — that baseline consumes energy every hour whether you leave the bed or not. Lie perfectly still for a full day and you would still burn roughly your BMR. For most adults it accounts for 60 to 70 per cent of all calories used in a day, which is why it sits underneath every diet plan, calorie target, and fitness programme. People look it up when they want to understand why their maintenance calories are what they are, when a dietitian asks for the figure, or when two friends of the same weight discover they need very different amounts of food. The tool takes four inputs — age, gender, height, and weight — and applies the Mifflin-St Jeor equation, published in 1990 and validated by a 2005 evidence review from the American Dietetic Association as the most accurate predictive equation for estimating resting metabolic rate in the general adult population. For men: BMR = 10 × weight in kg + 6.25 × height in cm − 5 × age + 5. For women the last term is −161 rather than +5, reflecting typical differences in lean mass. Weight carries the most influence, height a moderate amount, and age pulls the figure down by 5 calories for every year, which is the arithmetic behind the familiar complaint that eating habits that worked at 25 cause weight gain at 45. Work through a real profile. A 30-year-old man weighing 80 kg at 180 cm: 10 × 80 = 800, plus 6.25 × 180 = 1,125, minus 5 × 30 = 150, plus 5. The total is 1,780 calories per day at complete rest. Multiply by a moderate activity factor of 1.55 and his full daily burn is roughly 2,759 calories. Compare a 28-year-old woman at 60 kg and 165 cm: 600 + 1,031.25 − 140 − 161 gives 1,330 calories. The 450-calorie gap between those two people is not a difference in discipline; it is body size, sex, and the formula doing its job. That number becomes useful in specific situations. A coach setting up a cutting phase for a client needs BMR first so the deficit is taken from TDEE and never dips below the resting requirement. Someone tracking a plateau can see whether the calories they are eating have quietly fallen under their BMR, which tends to bring fatigue, poor sleep, and lost muscle rather than faster fat loss. A person who has dropped 15 kg recalculates and finds their BMR has fallen by around 150 calories, explaining why the same diet no longer produces the same weekly drop. A lifter comparing two training blocks uses the muscle-mass effect as an argument for keeping resistance work in the plan, since lean tissue costs more to maintain at rest than fat does. The honest caveats matter here. Mifflin-St Jeor is a population average and cannot see your thyroid function, medication, sleep debt, or exact body composition, so real resting metabolism can sit a few hundred calories either side of the estimate. It also does not use body-fat percentage, which means a very muscular person is usually under-estimated and someone carrying a lot of fat is often over-estimated; the Katch-McArdle formula suits those cases better. The mistake to avoid is treating BMR as your eating target — it is a floor, not a goal, and eating at BMR while also training leaves you in a much steeper deficit than you intended. The equation is built for adults and is not appropriate for children, pregnant or breastfeeding women, or people managing medical conditions without professional input. None of this is medical advice; speak to a doctor or registered dietitian before big changes. The calculation runs entirely in your browser, so your measurements never leave your device.

BMR Calculator Formula & Method

Learn More — BMR Calculator Guide

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