BMR Calculator

What is BMR?

Your Basal Metabolic Rate (BMR) is the energy your body uses to keep vital functions running — breathing, circulation, cell production — while you're completely at rest. It typically accounts for 60–70% of the calories you burn each day.

BMR vs TDEE

BMR is rest only. Once you add daily movement and exercise, you get your TDEE — the number you actually use to plan fat loss or muscle gain. The panel above shows your TDEE across common activity levels.

How BMR is calculated, step by step

This calculator uses the Mifflin-St Jeor equation, published in 1990 and now the one most dietitians use for healthy adults. It takes weight, height and age, then applies a sex correction:

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

Worked example

A 30-year-old man, 80 kg (176 lb), 178 cm (5'10"): 10 × 80 = 800; 6.25 × 178 = 1,112.5; 5 × 30 = 150. Adding up, 800 + 1,112.5 − 150 + 5 = 1,768 kcal per day. A 35-year-old woman, 65 kg (143 lb), 165 cm (5'5") gets 650 + 1,031 − 175 − 161 = 1,345 kcal.

Age counts for little per year (5 kcal) but it adds up: ten years older means about 50 kcal less per day. Each kilogram adds 10 kcal — muscle or fat alike, because the formula can't tell them apart.

What BMR doesn't account for

No equation measures your actual metabolism; it estimates the average for people with your measurements. Two people with the same stats can differ by 10% or more. The biggest reasons:

• Muscle mass: people who have lifted for years usually run above the prediction. Muscle burns more at rest than fat.
• Long diets: after months in a deficit the body saves some energy (metabolic adaptation). The effect is usually small, but real.
• Thyroid, sleep and medication: hormonal changes and some drugs shift resting expenditure. If that applies to you, work with a professional.

Putting the number to use

BMR alone doesn't tell you how much to eat — it's the floor of your expenditure, before any movement. The number to plan a diet with is your TDEE, which multiplies BMR by your activity level. In the example above, the man with a 1,768 kcal BMR burns about 2,430 kcal on a lightly active day (factor 1.375).

Treat BMR as a safety reference: eating far below it for long stretches tends to cost muscle, energy and consistency. For fat loss, a moderate deficit from TDEE works better — the calorie deficit calculator does that math and never goes below 1,500 kcal (men) or 1,200 kcal (women).

Finally, treat the result as a starting point. Follow it for two or three weeks, track your weekly average weight, and adjust by 100–200 kcal if the trend doesn't match. Your own body is the best measuring device.

Frequently asked questions