Calculate your resting metabolic rate (RMR) — the calories your body burns at complete rest — using 5 validated formulas. Compare results, see your full TDEE at every activity level, and understand the science behind your metabolism.
Your Resting Metabolic Rate
RMR (Mifflin-St Jeor)—
TDEE (Sedentary)—
TDEE (Moderate)—
Calories/Day at Rest—
RMR Formula Comparison
Formula
RMR (kcal/day)
Accuracy
Best For
TDEE by Activity Level (Mifflin-St Jeor)
Activity Level
Multiplier
TDEE (kcal/day)
Description
Where Do Your RMR Calories Go?
Organ / System
% of RMR
Approximate kcal/day
RMR vs BMR: Key Differences
Basal Metabolic Rate (BMR) is measured under strict conditions: 12-hour fast, lying still, thermoneutral environment (no calorie burning for thermoregulation). It represents the absolute minimum calories to sustain basic life functions.
Resting Metabolic Rate (RMR) is measured without the strict fasting requirement and is typically 10–20% higher than BMR. It is more practical to use in real-world calorie planning.
For most people and most purposes, RMR is the more relevant number. Multiplied by an activity factor, it gives TDEE — your total daily calorie expenditure.
Factors That Affect RMR
Muscle mass — the biggest controllable factor; muscle burns ~3× more calories than fat at rest
Age — RMR declines ~1-2%/decade due to sarcopenia
Sex — males average 5–10% higher RMR due to greater lean mass
Thyroid function — thyroid hormones are the primary RMR regulator
Diet history — severe calorie restriction adapts metabolism downward
Frequently Asked Questions
RMR (Resting Metabolic Rate) is the calories your body burns at rest to maintain basic functions like breathing, circulation, and organ function. BMR (Basal Metabolic Rate) is measured under stricter lab conditions (fasted, motionless, post-sleep). In practice the two terms are used interchangeably — RMR is typically 10–20 calories higher than BMR for the same person.
Multiply your RMR by an activity factor to estimate total daily calorie needs (TDEE): sedentary (1.2), light activity (1.375), moderate activity (1.55), very active (1.725). To lose about 1 pound per week, subtract 500 calories from TDEE. To gain muscle, add 250–500 calories. Never eat below your RMR for extended periods — it causes muscle loss and metabolic adaptation.
Muscle mass is the largest factor — more muscle = higher RMR. Age reduces RMR by about 2–3% per decade after 30. Men have higher RMR than women due to greater lean mass. Thyroid disorders, sleep deprivation, and prolonged calorie restriction can all lower RMR. Strength training is the most effective way to maintain or increase RMR as you age.
Using Mifflin-St Jeor: RMR = 10 × 79.4 kg + 6.25 × 177.8 cm − 5 × 30 + 5 = 794 + 1,111 − 150 + 5 = 1,760 kcal/day. TDEE at sedentary (×1.2) = 2,112 kcal; at moderately active (×1.55) = 2,728 kcal. To lose 1 lb/week, subtract 500 from TDEE: target 2,228 kcal/day with moderate activity. Never eat below the RMR of 1,760 — doing so would risk muscle loss and metabolic adaptation.
Eating below your RMR means you're not providing enough calories for basic organ function. The body responds by lowering thyroid hormone output, reducing non-exercise activity, and breaking down muscle for energy — a process called adaptive thermogenesis. Studies show this can reduce RMR by 10–15% beyond what is expected from weight loss alone. The practical result is a slower metabolism that makes future weight loss increasingly difficult.