BMR Calculator

How to use the BMR calculator

Your basal metabolic rate (BMR) is the energy your body would use in a day lying completely at rest: breathing, pumping blood, keeping warm and running your brain and organs. The calculator works it out from four details.

1. Choose metric or US units (feet, inches and pounds work too) and your sex.
2. Enter your age, height and weight. It’s designed for adults aged 18 to 80.
3. Read your BMR, labelled “BMR (at complete rest)”, under the main result.

The large number at the top is your daily calories including activity (your TDEE); set the activity level to match a typical week.

The BMR formula used

The calculator uses the Mifflin-St Jeor equation, published in the American Journal of Clinical Nutrition in 1990 and widely used by dietitians:

• Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
• Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

Worked example (woman): 45 years, 165 cm, 60 kg. 600 + 1,031.25 − 225 − 161 = 1,245 kcal a day.

Worked example (man): 30 years, 180 cm, 80 kg. 800 + 1,125 − 150 + 5 = 1,780 kcal a day.

What raises or lowers your BMR

The equation shows how each factor moves the result:

So the same man at 25, 45 and 65 has an estimated BMR of 1,805, 1,705 and 1,605 kcal. Real bodies differ from the average: people with more muscle usually burn more at rest than the equation predicts, because muscle uses more energy than fat. Thyroid conditions, some medicines, illness and pregnancy also change it.

BMR vs TDEE vs RMR

• BMR (basal metabolic rate): energy at complete rest, measured in strict lab conditions after fasting and sleep.
• RMR (resting metabolic rate): energy at rest in everyday conditions, usually a little higher than BMR. Many calculators use the two terms interchangeably.
• TDEE (total daily energy expenditure): BMR plus everything you do, from walking to exercise. It’s BMR × an activity factor from 1.2 to 1.9.

Your BMR is not a calorie target: eating only your BMR would mean eating less than your body uses on any normal day. For a daily figure, use your TDEE; the TDEE calculator explains the activity levels in detail.

Other BMR equations

You may see slightly different numbers elsewhere, because other equations exist. The Harris-Benedict equation (first published in 1919, revised in 1984) tends to give somewhat higher results for many people. The Katch-McArdle formula uses lean body mass instead of weight, so it needs your body-fat percentage. Mifflin-St Jeor was found to be among the most accurate for adults in a review by the American Dietetic Association (Frankenfield and colleagues, 2005), which is why the calculator uses it. All of them are estimates; only a lab measurement such as indirect calorimetry measures your actual rate.

Using your BMR well

• As a floor of understanding, not a diet. It’s the energy your body needs just to keep going.
• To understand weight change. As you lose weight, your BMR falls (10 kcal per kg in the equation), which is one reason progress slows.
• To compare with your activity. TDEE minus BMR is roughly what your daily movement and exercise add.

Very low-calorie diets should only be followed with medical supervision; the NHS explains how calories work for everyday eating. Your BMI gives a different, complementary picture of your weight, and kg to lbs helps if your scale uses the other unit.

Ask in plain words

• “What’s my BMR? Woman, 45, 165 cm, 60 kg.”
• “BMR for a 30-year-old man, 5 ft 11 in, 176 lb.”
• “How much does my BMR drop if I lose 5 kg?”

Type it under the calculator or in the AI workspace. Nothing you enter is stored or used to train AI.