Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to keep you alive — fueling your heart, lungs, brain, and every cell. It forms the foundation of any nutrition plan and typically accounts for 60–75% of your total daily energy expenditure. This calculator compares three leading formulas so you can see which is most relevant to your body composition.
Calculate Your BMR
Optional: Enter your body fat % to unlock the Katch-McArdle formula, which is more accurate for athletes and those with known body composition.
BMR by Formula
All values are estimates. Individual metabolism varies.
Daily Calorie Needs by Activity Level
Based on your Mifflin-St Jeor BMR. Multiply by your activity factor to find how many calories you need to maintain your current weight.
| Activity Level | Multiplier | Calories/day |
|---|
What your BMR means
How to Use the BMR Calculator
Your Basal Metabolic Rate is the single most important number in any nutrition strategy. Whether you want to lose fat, build muscle, or simply maintain your current weight, everything starts with knowing how many calories your body burns at rest. This calculator gives you three independent estimates so you can choose the formula that best matches your situation.
Step 1: Enter Your Stats
Fill in your age, gender, weight, and height. You can switch between metric (kg / cm) and imperial (lbs / ft + in) using the toggle at the top. The calculator automatically converts between units internally, so there is no need to do any manual conversion.
Step 2: Add Body Fat % (Optional)
If you know your body fat percentage from a DEXA scan, hydrostatic weighing, or a reliable skinfold test, enter it in the optional field. This unlocks the Katch-McArdle formula, which calculates BMR from lean body mass rather than total weight. For athletes, bodybuilders, or anyone with a body composition that differs significantly from average, this formula is typically the most accurate of the three.
Step 3: Read Your Formula Results
The calculator displays your BMR from three formulas side by side:
- Mifflin-St Jeor — the recommended formula for most adults, validated in 1990 and endorsed by the Academy of Nutrition and Dietetics
- Harris-Benedict (Revised) — the classic formula, updated in 1984; results are typically 5% higher than Mifflin-St Jeor
- Katch-McArdle — the most precise formula if you know your body fat percentage; ignores the bias introduced by excess or insufficient fat mass
Step 4: Use the Activity Table
The activity-level table multiplies your Mifflin-St Jeor BMR by standard activity factors — from Sedentary (1.2) up to Athlete (1.9). The resulting number is your estimated maintenance calorie intake at that activity level. To lose weight, eat 300–500 calories below your maintenance level. To build muscle, eat 200–300 calories above it.
How the Formulas Are Calculated
For reference, here are the exact equations used:
- Mifflin-St Jeor: Male =
10W + 6.25H − 5A + 5· Female =10W + 6.25H − 5A − 161 - Harris-Benedict (Revised): Male =
13.397W + 4.799H − 5.677A + 88.362· Female =9.247W + 3.098H − 4.330A + 447.593 - Katch-McArdle:
370 + 21.6 × LBMwhere LBM = weight × (1 − body fat %)
W = weight in kg, H = height in cm, A = age in years, LBM = lean body mass in kg.
FAQ
Is this BMR calculator free to use?
Yes, this BMR calculator is completely free with no limits. You can run as many calculations as you want using any of the three formulas. No signup is required and everything runs locally in your browser.
Is my personal data safe and private?
Yes, all calculations happen entirely in your browser using client-side JavaScript. Your age, weight, height, and body fat percentage are never sent to a server, never stored remotely, and never shared with anyone.
What is Basal Metabolic Rate (BMR)?
BMR is the number of calories your body burns at complete rest to maintain essential functions like breathing, circulation, and cell production. It represents the minimum energy needed to keep you alive and typically accounts for 60 to 75 percent of total daily calorie expenditure.
Which BMR formula is the most accurate?
The Mifflin-St Jeor equation is considered the most accurate for most people and is recommended by the Academy of Nutrition and Dietetics. The revised Harris-Benedict is slightly older but still widely used. The Katch-McArdle formula is the most precise if you know your body fat percentage, because it accounts for lean body mass directly.
What is the difference between BMR and TDEE?
BMR is the calories your body needs at rest, while TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor. TDEE represents the total calories you actually burn in a day including exercise and movement. BMR is always lower than TDEE.
How does the Katch-McArdle formula work?
The Katch-McArdle formula calculates BMR from lean body mass rather than total weight. The formula is BMR = 370 + (21.6 times lean body mass in kg). Lean body mass equals your total weight multiplied by one minus your body fat percentage as a decimal. This makes it more accurate for athletes or people with high or low body fat.
What activity level should I choose?
Choose Sedentary if you have a desk job and barely exercise. Light Activity means 1 to 3 days of light exercise per week. Moderate Activity is 3 to 5 days per week. Active means hard exercise 6 to 7 days per week. Athlete level is for people who train twice daily or have physically demanding jobs combined with regular training.
How often should I recalculate my BMR?
Recalculate your BMR whenever your weight changes by 5 pounds or more, or if your activity level changes significantly. BMR also decreases slightly with age, so an annual recalculation is a good habit. Significant muscle gain will also increase your BMR, which is why strength training boosts long-term metabolism.