Resting Metabolic Rate (RMR) is the number of calories your body burns at rest to maintain basic functions like breathing, circulation, and cell production. It's the largest component of daily energy expenditure for most people, accounting for 60–75% of total calories burned. Understanding your RMR is the foundation for building an accurate nutrition or weight loss plan.
The Formula (Mifflin-St Jeor)
This is the most accurate modern formula:
RMR (men) = (10 × weight_kg) + (6.25 × height_cm) - (5 × age_years) + 5
RMR (women) = (10 × weight_kg) + (6.25 × height_cm) - (5 × age_years) - 161
Result is in kilocalories per day.
Worked Example
A 30-year-old woman, 70 kg, 165 cm:
RMR = (10 × 70) + (6.25 × 165) - (5 × 30) - 161
= 700 + 1031.25 - 150 - 161
= 1,420 calories/day
She burns about 1,420 calories per day at rest.
RMR by Age and Gender
| Age | Average RMR Men | Average RMR Women |
|---|---|---|
| 20–30 years | 1,900–2,000 | 1,550–1,650 |
| 30–40 years | 1,850–1,950 | 1,500–1,600 |
| 40–50 years | 1,800–1,900 | 1,450–1,550 |
| 50–60 years | 1,700–1,800 | 1,350–1,450 |
| 60+ years | 1,600–1,700 | 1,250–1,350 |
RMR declines with age due to loss of muscle mass.
Total Daily Energy Expenditure
RMR is just the baseline. Total calories burned depends on activity:
TDEE = RMR × Activity Factor
| Activity Level | Factor |
|---|---|
| Sedentary (little exercise) | 1.2 |
| Lightly active (1–3 days/week) | 1.375 |
| Moderately active (3–5 days/week) | 1.55 |
| Very active (6–7 days/week) | 1.725 |
| Extremely active (professional athlete) | 1.9 |
For the example woman, if moderately active: TDEE = 1,420 × 1.55 = 2,201 calories/day.
Factors Affecting RMR
- Muscle mass: Increases RMR (muscle burns more at rest than fat)
- Age: Decreases RMR (about 2–3% per decade after 30)
- Genetics: 10–20% variation between individuals
- Hormones: Thyroid disorders, menopause, stress all affect RMR
- Diet: Chronic undereating reduces RMR (adaptive thermogenesis)
Tips
RMR is most accurately measured via indirect calorimetry in a lab, but the formula is reliable for most people (±10%). To increase RMR, build muscle through resistance training. Crash dieting lowers RMR, making weight loss harder — another reason steady, moderate calorie deficits are preferable.
Use our Resting Metabolic Rate Calculator to estimate your daily calorie burn at rest.