BMR Calculator

This BMR calculator estimates your Basal Metabolic Rate — the number of calories your body burns at complete rest just to keep you alive. That energy powers breathing, circulation, cell repair, brain activity, hormone production, and temperature regulation, even on a day when you never leave your bed. It is the single most useful starting number for anyone planning to lose fat, gain muscle, or simply eat the right amount, because it tells you the floor your daily calories should rarely drop below.

It is built for gym-goers, people on a weight-loss or weight-gain journey, anyone tracking calories with a diet app, and the simply curious who want to understand their own metabolism. Once you know your BMR, this tool also shows your TDEE (Total Daily Energy Expenditure) across five activity levels, so you can see roughly how many calories you actually burn on an average day, not just at rest.

The formulas this calculator uses

The recommended method is the Mifflin-St Jeor equation, published in 1990 and considered the most accurate predictive formula for the general population. You can also switch to the original 1919 Harris-Benedict equation for comparison.

Mifflin-St Jeor

Men: BMR = 10W + 6.25H − 5A + 5

Women: BMR = 10W + 6.25H − 5A − 161

Harris-Benedict (original 1919)

Men: BMR = 88.4 + 13.4W + 4.8H − 5.7A

Women: BMR = 447.6 + 9.2W + 3.1H − 4.3A

Where W = weight (kg), H = height (cm), A = age (years). Notice that weight, height, and (for men) a positive constant push the number up, while age pushes it down — metabolism naturally slows as we get older, largely because muscle mass declines.

Worked example

Take a 30-year-old man weighing 75 kg at 178 cm, using Mifflin-St Jeor. The maths is (10 × 75) + (6.25 × 178) − (5 × 30) + 5 = 750 + 1,112.5 − 150 + 5 = 1,717 calories per day at complete rest. To find his TDEE we multiply by an activity factor: at a moderately active level (×1.55) that becomes about 2,662 calories a day. If he wanted to lose fat, a 500-calorie daily deficit would put his target near 2,162 calories.

BMR vs TDEE, and how to use the numbers

BMR is what you burn doing nothing; TDEE is what you burn living your real life. For most people TDEE lands between 1.3 and 1.9 times BMR. To lose weight, eat below your TDEE; to gain, eat above it. A common, sustainable approach is a deficit or surplus of 300–500 calories a day, which is gentle enough to be maintainable.

Choosing your activity factor

To turn BMR into TDEE this tool multiplies by a standard activity factor, and the results panel shows all five at once so you can find the one that fits your week. Sedentary (×1.2) suits a desk job with little or no exercise. Lightly active (×1.375) fits light exercise one to three days a week. Moderately active (×1.55) matches moderate exercise three to five days. Very active (×1.725) is for hard exercise six to seven days a week, and extra active (×1.9) covers a physically demanding job or two training sessions a day. When in doubt, pick the lower of two options — it is easier to add calories later than to discover you have been eating too many.

Tips and common mistakes

Pick your activity level honestly — most people overestimate it, which is the number-one reason a "calculated" deficit fails to produce results. Eating below your BMR for long stretches is another mistake: it can stall progress, cost you muscle, and leave you tired. Two formulas give slightly different answers, so stick with one for consistency rather than switching to whichever reads higher. Remember that these equations assume an average body composition; very muscular or very lean people will see their true BMR differ from the estimate.

This is a general fitness screening tool, not medical or dietary advice. Your real metabolism can vary by 10–15% from any formula because of body composition, genetics, thyroid function, and other factors. Before starting an aggressive diet, or if you have a medical condition, are pregnant, or are recovering from illness, consult a doctor or a registered dietitian.