Resting Metabolic Rate Calculator

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.