Resting Metabolic Rate Calculator
Calculate your resting metabolic rate (RMR) — the number of calories your body burns at complete rest just to keep you alive. RMR is the foundation for every accurate calorie goal, whether you are cutting, bulking, or maintaining.
What Is Resting Metabolic Rate?
Resting metabolic rate (RMR) is the number of calories your body burns in a 24-hour period while completely at rest — no activity, no digestion of a large meal, just the energy required to keep your heart beating, lungs breathing, brain working, and cells regenerating. For most people, RMR accounts for 60-75% of total daily calories burned. Understanding your RMR tells you the minimum calories you need before any movement or exercise is added. This calculator uses the Mifflin-St Jeor equation, the most accurate general-population formula according to the Academy of Nutrition and Dietetics.
RMR vs BMR — Are They the Same?
RMR and BMR (basal metabolic rate) are often used interchangeably but have a small technical difference. BMR is measured under strict laboratory conditions — 12 hours fasted, fully rested, in a thermoneutral room. RMR is measured under less rigid conditions and includes a small amount of post-meal digestion and involuntary movement. In practice, RMR is typically 5-10% higher than true BMR. For everyday calorie planning, the values are close enough that this tool uses Mifflin-St Jeor, which technically estimates BMR but is commonly labeled RMR in nutrition software.
How to Use RMR for Weight Goals
Your RMR is the starting point. To get total daily energy expenditure (TDEE), multiply RMR by an activity factor: 1.2 (sedentary), 1.375 (light exercise 1-3 days/week), 1.55 (moderate 3-5 days), 1.725 (heavy 6-7 days), or 1.9 (very heavy physical job plus training). For fat loss, most people subtract 300-500 calories from TDEE for a sustainable 0.5-1 lb per week loss. For muscle gain, add 200-400 calories. Never eat below your RMR for extended periods — doing so slows metabolism, reduces muscle, and typically causes rebound weight gain.
What Affects RMR?
The biggest driver of RMR is lean body mass (muscle and organs). More muscle means higher RMR, which is why strength training is so valuable for long-term weight control. Other factors: age (RMR drops about 2-3% per decade after 20), sex (men typically have higher RMR due to greater muscle mass), genetics (up to 15% variation between individuals of the same size), hormones (thyroid conditions change RMR significantly), and severe dieting (extended under-eating suppresses RMR by 10-20%). Body fat percentage matters less than people assume — at the same total weight, a lean person has a higher RMR than a higher-body-fat person.
Frequently Asked Questions
What is a normal resting metabolic rate?
Average RMR ranges from about 1,400-1,800 kcal/day for adult women and 1,600-2,100 kcal/day for adult men, varying with size, age, and body composition. A 30-year-old 5'6" 150 lb woman has an RMR around 1,400 kcal. A 30-year-old 5'10" 180 lb man has an RMR around 1,800 kcal.
Which equation is most accurate for RMR?
The Mifflin-St Jeor equation is the current gold standard for general populations and is what this calculator uses. It is more accurate than the older Harris-Benedict equation, with a typical margin of error of about 10% against indirect calorimetry (lab gold standard).
Can I increase my RMR?
Yes, modestly. Adding muscle through strength training raises RMR because muscle is more metabolically active than fat — about 6 kcal per pound of muscle per day at rest. Eating enough protein (0.7-1g per pound of bodyweight) and avoiding prolonged severe caloric deficits also protects RMR over time.
Does RMR decrease with age?
Yes. RMR declines roughly 2-3% per decade starting around age 20, largely because people lose muscle mass with age (sarcopenia). Strength training and adequate protein intake can blunt this decline significantly. By age 60, a sedentary adult may have 300-400 fewer calories of maintenance than at 25.
How does RMR relate to TDEE?
TDEE (total daily energy expenditure) = RMR × activity factor. RMR is the resting baseline; TDEE includes everything else — walking, exercise, fidgeting, digestion. RMR is usually 60-75% of TDEE. This calculator returns both values so you can base calorie goals on TDEE but never eat below RMR long-term.
Should I eat below my RMR to lose weight faster?
No. Eating below RMR for extended periods triggers metabolic adaptation — your body suppresses RMR by 10-20% to conserve energy, making further weight loss harder and often causing muscle loss. Target a moderate deficit below TDEE (typically 300-500 kcal) but stay above RMR for sustainable results.