BMR Calculator

All three equations estimate the energy used at rest from things that are easy to measure. They give slightly different answers because they were built from different groups of people. Mifflin-St Jeor was published in 1990 and, in comparisons with measured metabolism, predicts BMR within about 10 percent for most healthy adults, which is why it is the default here.

BMR covers rest only. The calories you actually burn in a day, called total daily energy expenditure (TDEE), add everything you do: walking, work, exercise and even digesting food. A simple and widely used way to estimate it is to multiply BMR by an activity factor: 1.2 if you sit most of the day, 1.375 for light exercise one to three days a week, 1.55 for moderate exercise three to five days, 1.725 for hard exercise six or seven days, and 1.9 for a physical job plus training. The table under the results shows all five, so you can pick the line that fits your week.

For a full plan with calorie targets for losing or gaining weight, use the TDEE Calculator or the Calorie Deficit Calculator; both start from the same BMR.

Bigger bodies use more energy, so BMR rises with height and weight. Muscle uses more energy than fat, which is why men, who on average carry more muscle, have a higher BMR at the same size, and why the Katch-McArdle formula, which only looks at lean mass, can be more accurate for very muscular or very lean people. BMR slowly falls with age, mostly because muscle mass tends to fall; strength training helps keep it.

Other things the formulas can't see also matter: thyroid function, some medicines, pregnancy and breastfeeding, recent illness, very low calorie dieting (the body adapts by using less energy) and genetics. Two people with the same numbers can differ by a few hundred calories a day.

Treat your BMR as an estimate, not a target to eat. Eating less than your BMR for a long time is rarely a good idea without medical supervision, because it makes it hard to get enough protein, vitamins and minerals and can slow your metabolism. The most reliable way to fine-tune any estimate is to track your weight and what you eat for two or three weeks, then adjust: if your weight stays the same, the calories you ate are close to your real daily needs.