BMR Explained: How Many Calories Your Body Burns at Rest

ExaCalc Team

October 5, 2026

6 min read

bmrmetabolismcalorieshealthfitness

BMR Explained: How Many Calories Your Body Burns at Rest

Even if you spent the whole day in bed, your body would burn calories to keep your heart beating, your lungs working and your temperature steady. That minimum is your basal metabolic rate, or BMR, and it is the starting point for every sensible calorie target.

What BMR Is, and What It Is Not

BMR is the energy your body uses at complete rest, in a neutral environment, after fasting. In practice, most calculators estimate resting metabolic rate (RMR), which is very close and slightly easier to measure. For everyday planning the two are treated as the same.

BMR is not your total daily burn. Movement, exercise and digestion add to it. Total daily energy expenditure, or TDEE, is what you actually burn, and it is covered in our guide to TDEE and calorie needs.

The Mifflin-St Jeor Equation

The BMR Calculator uses the Mifflin-St Jeor equation, widely regarded as one of the more accurate formulas for the general adult population:

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

Weight in pounds? Multiply by 0.4536. Height in inches? Multiply by 2.54.

Worked Example: A Man

Age 30, weight 80 kg, height 180 cm.

10 × 80 = 800
6.25 × 180 = 1,125
5 × 30 = 150
BMR = 800 + 1,125 − 150 + 5 = 1,780 kcal per day

Worked Example: A Woman

Age 28, weight 62 kg, height 165 cm.

10 × 62 = 620
6.25 × 165 = 1,031.25
5 × 28 = 140
BMR = 620 + 1,031.25 − 140 − 161 = 1,350 kcal per day (1,350.25 before rounding)

From BMR to Daily Calories

Multiply BMR by an activity factor to estimate TDEE. The usual multipliers are:

Sedentary (desk job, little exercise): 1.2
Lightly active (exercise 1 to 3 days a week): 1.375
Moderately active (3 to 5 days a week): 1.55
Very active (6 to 7 days a week): 1.725
Extremely active (physical job plus training): 1.9

The man above, moderately active: 1,780 × 1.55 = about 2,759 kcal per day to maintain his weight. The woman, lightly active: 1,350 × 1.375 = about 1,856 kcal per day.

Use the TDEE Calculator to apply these factors automatically, and the Calorie Calculator to set a target for losing or gaining weight.

What Changes Your BMR

Body size: larger bodies burn more, which is why weight and height both appear in the formula.
Muscle: lean tissue burns more energy at rest than fat tissue, so someone with more muscle at the same weight has a higher BMR. The formula does not see this, so it can underestimate for muscular people.
Age: BMR tends to fall with age, partly through loss of muscle. The formula reflects this through the age term.
Sex: men on average have more lean mass, hence the different constants.
Illness, pregnancy, thyroid conditions and some medications: these can shift BMR in ways no formula captures.

How Accurate Is It?

It is an estimate. The equation was built from population data, so any individual can differ from it by a noticeable margin. Treat the output as a starting point, track your weight and intake for two to three weeks, and adjust. If your weight is stable on the estimated number, it was close. If not, change it by 100 to 200 calories and observe again.

Using BMR Safely

Eating below your BMR for long periods is generally not recommended without professional supervision. It can lead to muscle loss, fatigue and nutrient gaps.
A modest deficit of roughly 300 to 500 calories below TDEE is a commonly used starting point for gradual weight loss, but individual needs vary.
If you have a medical condition, are pregnant, are under 18, or are older, ask a doctor or registered dietitian.

Pair It With Your Other Numbers

BMR is one input among several. Your BMI gives a rough size category, and the Macro Calculator turns a calorie target into protein, carbohydrate and fat amounts. See our macro guide for how to split them.