Basal metabolic rate is the calorie cost of keeping the body alive: breathing, circulation, temperature control and cell maintenance. The National Academies' 2023 Dietary Reference Intakes for Energy describe it as the energy required when the body is at complete physical, mental and digestive rest, typically measured after waking and at least 12 hours after the last meal. The closely related resting metabolic rate (RMR, or resting energy expenditure) is measured under slightly looser conditions: awake, resting, after a few hours without food or exercise, at a comfortable temperature. In everyday use the two terms are often treated as interchangeable, and most calculators estimate RMR.
According to the same report, resting energy expenditure typically accounts for 60 to 70 percent of total daily energy expenditure.
Formula
BMR is measured in a lab by indirect calorimetry. Outside a lab it is estimated with a prediction equation. The Mifflin-St Jeor equation is a widely used choice:
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (y) + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (y) − 161
The result is in kilocalories per day.
Example
A 35-year-old woman who weighs 68 kg and is 165 cm tall:
- 10 × 68 = 680
- 6.25 × 165 = 1,031.25
- 5 × 35 = 175
- BMR = 680 + 1,031.25 − 175 − 161 ≈ 1,375 kcal/day
The BMR calculator runs this estimate, and the macro calculator and protein calculator build daily targets from it. The guide to calculating macros shows the full sequence from BMR to grams.
Common mistakes
- Eating to BMR as if it were a daily calorie need. BMR excludes digestion and all physical activity, so total needs are higher.
- Treating a formula result as a measurement. Equations estimate the average for people with similar weight, height, age and sex; individuals can differ.