Your Resting Metabolic Rate (RMR) is the number of calories your body burns at rest over 24 hours to keep your organs functioning. Unlike a lab measurement, this calculator uses the clinically validated Mifflin-St Jeor and Katch-McArdle equations to estimate your RMR and project your Total Daily Energy Expenditure (TDEE) at any activity level.
Calculate Your RMR
Optional: Enter your body fat % to unlock the Katch-McArdle formula, which is more accurate for athletes and people with known body composition.
RMR by Formula
All values are estimates. Individual metabolism varies by genetics and body composition.
Your TDEE at Every Activity Level
Based on your Mifflin-St Jeor RMR. Your selected activity level is highlighted.
| Activity Level | TDEE (kcal/day) |
|---|
What this means for your goals
How to Use the RMR Calculator
Your Resting Metabolic Rate is the foundation of any effective nutrition plan. Whether you are losing fat, building muscle, or maintaining your weight, you need an accurate baseline calorie number. This calculator gives you two independently validated estimates so you can cross-check your results.
Step 1: Enter Your Stats
Fill in your sex, age, weight, and height. Toggle between metric (kg/cm) and imperial (lbs/ft+in) units at the top. Sex matters because men and women have different average muscle-to-fat ratios, which affects the formula constants.
Step 2: Add Body Fat % for More Precision
If you know your body fat percentage from a DEXA scan, skinfold calipers, or a validated bioelectrical impedance device, enter it in the optional field. This enables the Katch-McArdle formula: RMR = 370 + 21.6 × lean body mass (kg). This formula ignores the sex and age constants because lean mass already captures those differences, making it the most accurate option for athletes.
The Mifflin-St Jeor Formula Explained
The Mifflin-St Jeor equation (1990) is:
- Men:
10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 - Women:
10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
It was validated against measured RMR in 498 subjects and is accurate to within ±10% for 82% of people — the highest accuracy of any non-body-composition formula.
Step 3: Choose Activity Level for TDEE
Select your typical activity level to multiply your RMR into a Total Daily Energy Expenditure estimate. Most people underestimate their activity level — choose honestly. The TDEE table shows all five levels so you can see the full range of your calorie needs.
Using RMR for Weight Goals
Your TDEE at your selected activity level is your maintenance calorie intake. To lose weight, eat 300–500 kcal below your TDEE. To build muscle, eat 200–300 kcal above TDEE. To maintain weight, eat at TDEE. Avoid eating below your RMR for extended periods — doing so risks muscle loss and metabolic adaptation.
FAQ
Is this RMR calculator free?
Yes, completely free. No signup required and all calculations happen locally in your browser. Your personal data is never sent to a server.
What is Resting Metabolic Rate (RMR)?
RMR is the number of calories your body burns at rest over 24 hours to maintain basic functions like breathing, circulation, and cell repair. It is similar to BMR but measured under slightly less strict conditions — RMR is typically 10-20% higher than true BMR because it includes the thermic effect of recent food and some light movement.
What is the difference between RMR and BMR?
Basal Metabolic Rate (BMR) is measured in a completely fasted, rested state. Resting Metabolic Rate (RMR) is measured under normal resting conditions, so it is slightly higher (usually 10-20%) than BMR. In practical use, the terms are often used interchangeably since the Mifflin-St Jeor equation is used for both.
Which formula should I use — Mifflin-St Jeor or Katch-McArdle?
Mifflin-St Jeor is the most widely validated formula for general use and is recommended by the Academy of Nutrition and Dietetics. Katch-McArdle is more accurate for people who know their body fat percentage, especially athletes, because it calculates RMR from lean body mass and ignores excess fat mass bias.
How do I calculate my TDEE from RMR?
Multiply your RMR by an activity factor: sedentary (×1.2), lightly active (×1.375), moderately active (×1.55), very active (×1.725), or extremely active (×1.9). The result is your Total Daily Energy Expenditure — the number of calories you burn per day including all activity.
How accurate is an online RMR calculator?
Online calculators using validated equations like Mifflin-St Jeor are accurate to within ±10% for most people. The Katch-McArdle formula (with body fat %) is more accurate for athletes. Lab-measured RMR via indirect calorimetry is the gold standard but requires clinical equipment.
Can I improve my resting metabolic rate?
Yes. Resistance training is the most effective way to increase RMR because it builds lean muscle mass, which burns more calories at rest (roughly 6-10 kcal/day per pound of muscle). Eating adequate protein also helps preserve muscle during weight loss, preventing RMR decline.