BMR Calculator

What is BMR, and what does this tool calculate?

Basal metabolic rate: roughly the energy your body burns at complete rest, keeping your heart beating, lungs working and temperature stable. This tool uses the Mifflin-St Jeor equation, published in 1990, which takes weight in kilograms, height in centimetres, age in years and sex.

What is the actual formula?

10 × weight(kg) + 6.25 × height(cm) − 5 × age(years), then + 5 for men and − 161 for women. That is the whole calculation — you can check the result by hand.

Why does the formula only offer male and female?

Because Mifflin-St Jeor was derived with a single binary term, and that term is the only place sex enters the equation. The two variants differ by a fixed 166 kcal. If neither fits you, one common approach is to calculate both and treat the range between them as your estimate, then adjust based on what actually happens to your weight over a few weeks.

Why do other calculators give me a different number?

Different equations. Harris-Benedict is older and tends to read higher; Katch-McArdle uses lean body mass instead of total weight, so it needs a body fat estimate but handles very muscular or very lean people better. Mifflin-St Jeor is generally the default for the average adult, which is why it is used here. None of them is exact for an individual.

How accurate is it for me specifically?

Treat it as an estimate with meaningful error bars. Predictive equations are fitted to population averages, so an individual can sit noticeably above or below the prediction depending on lean mass, thyroid function, medication and genetics. The only way to know your real figure is indirect calorimetry in a lab. Use this number as a starting point and let your actual weight trend correct it.

Is BMR the same as the calories I should eat?

No — BMR is your at-rest floor, before any movement at all. What you actually burn in a day is your TDEE: BMR multiplied by an activity factor. Use the calorie and TDEE calculator for that, and never treat BMR as a target intake.

Does anything I type leave my device?

No. The equation runs in your browser; no inputs are transmitted or stored.

Can I use this to plan a diet?

Only as background reading. Energy intake, deficits and any medically relevant condition are matters for a doctor or a registered dietitian — particularly if you are pregnant, an athlete in training, or managing a condition like diabetes or thyroid disease.