BMR Calculator
Calculate your Basal Metabolic Rate online for free with our BMR calculator. Enter your age, sex, weight, and height to get your BMR from both the Mifflin-St Jeor and Harris-Benedict formulas side by side. Optionally add your body fat percentage for a Katch-McArdle estimate. Includes a TDEE reference table for all five activity levels — no signup required, all calculations run locally in your browser.
Enter your age, sex, weight, and height to calculate your Basal Metabolic Rate using both the Mifflin-St Jeor and Harris-Benedict equations. Optionally add your body fat percentage for a Katch-McArdle estimate. All calculations run instantly in your browser — no signup required.
Enables the Katch-McArdle formula — most accurate when body fat % is known.
Why Use Our BMR Calculator?
Instant BMR Calculations
Calculate your Basal Metabolic Rate instantly in your browser with zero wait time. Our BMR calculator runs both the Mifflin-St Jeor and Harris-Benedict formulas simultaneously and delivers results in milliseconds.
Secure BMR Calculator Online
All BMR calculations run locally in your browser. Your age, weight, height, and body fat percentage never leave your device, ensuring 100% privacy every time you use our BMR calculator online.
BMR Calculator - No Installation
Use our BMR calculator directly in any browser with no downloads, plugins, or software required. Calculate your basal metabolic rate from any device, completely free.
Three Formula Comparison
Our BMR calculator compares Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle (when body fat % is provided) side by side with a visual bar chart, plus a full TDEE reference table for all five activity levels.
Common Use Cases for BMR Calculator
Calorie Deficit Planning
Use our BMR calculator to find your baseline calorie burn before setting a calorie deficit for weight loss. Knowing your BMR ensures you never cut calories below the minimum your body needs to function.
Muscle Gain & Bulking
Bodybuilders and athletes use our BMR calculator to establish their maintenance calories before adding a calorie surplus for muscle gain. The TDEE reference table shows exact targets for each activity level.
Nutrition & Diet Planning
Dietitians and nutritionists use our BMR calculator to set evidence-based calorie targets for clients. The Mifflin-St Jeor and Harris-Benedict comparison helps identify the most appropriate formula for each individual.
Fitness Tracking & Progress
Fitness enthusiasts use our BMR calculator to recalculate their basal metabolic rate as their weight changes. Recalculating BMR every 4–6 weeks ensures calorie targets stay accurate throughout a transformation.
Medical & Clinical Reference
Healthcare professionals use our BMR calculator as a quick reference for estimating resting energy expenditure. The Katch-McArdle formula is particularly useful for patients with known body composition data.
Intermittent Fasting Planning
People following intermittent fasting protocols use our BMR calculator to ensure their eating window provides enough calories to meet their BMR. Eating below BMR for extended periods can impair metabolism.
Understanding BMR Calculations
What is a BMR Calculator?
A BMR calculator estimates your Basal Metabolic Rate — the number of calories your body burns at complete rest to maintain basic physiological functions like breathing, circulation, and cell repair. BMR is the foundation of all calorie calculations: your TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor. Our BMR calculator runs three industry-standard formulas — Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle — so you can compare results and choose the most appropriate estimate for your situation. All calculations run locally in your browser with no data sent to any server.
How Our BMR Calculator Works
- Enter Your Stats: Select your unit system (metric or imperial), biological sex, and enter your age, weight, and height. Optionally add your body fat percentage to unlock the Katch-McArdle formula for the most accurate result.
- Instant Multi-Formula Calculation: Click Calculate BMR and the calculator instantly runs the Mifflin-St Jeor, Harris-Benedict, and (if body fat % is provided) Katch-McArdle formulas. All calculations happen locally in your browser with complete privacy.
- Compare Results and Plan: View your BMR from each formula side by side with a visual comparison bar, then use the TDEE reference table to find your maintenance calories at any of five activity levels.
BMR Formulas Explained
- Mifflin-St Jeor (1990) — Recommended: Male: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. Female: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161. Developed in 1990, this is the most accurate formula for most adults and is the standard used by dietitians and fitness professionals.
- Harris-Benedict (Revised 1984): Male: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age). Female: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age). The original Harris-Benedict equation (1919) was revised by Roza and Shizgal in 1984 for improved accuracy.
- Katch-McArdle (Lean Mass Based): BMR = 370 + (21.6 × lean body mass in kg). Lean mass = weight × (1 − body fat%). This formula is sex-neutral and is the most accurate when body fat percentage is known, making it ideal for athletes and muscular individuals.
- TDEE = BMR × Activity Multiplier: Total Daily Energy Expenditure is your BMR multiplied by an activity factor: 1.2 (sedentary), 1.375 (lightly active), 1.55 (moderately active), 1.725 (very active), 1.9 (extra active). TDEE represents your actual daily calorie needs.
What the BMR Calculator Shows
- BMR (Mifflin-St Jeor): Your primary BMR estimate — the most accurate formula for most adults, displayed prominently.
- Formula Comparison Bar: A visual side-by-side comparison of all calculated BMR values so you can see how the formulas differ for your specific stats.
- Katch-McArdle BMR: Available when body fat % is entered — the most accurate formula for athletes and muscular individuals.
- TDEE Reference Table: Your estimated Total Daily Energy Expenditure at all five activity levels, calculated from your Mifflin-St Jeor BMR.
- Inputs Summary: A recap of the values used in the calculation for easy reference and verification.
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Frequently Asked Questions About BMR Calculator
A BMR calculator estimates your Basal Metabolic Rate — the number of calories your body burns at complete rest to maintain basic functions like breathing, circulation, and cell repair. Our BMR calculator runs the Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas simultaneously and delivers results instantly in your browser — no signup required.
BMR is the calories your body burns at complete rest — before any activity. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor to account for all movement and exercise. TDEE is always higher than BMR and represents your actual daily calorie needs. Our BMR calculator includes a TDEE reference table for all five activity levels.
The Mifflin-St Jeor equation (1990) is generally considered more accurate for most adults and is the standard recommended by the Academy of Nutrition and Dietetics. The Harris-Benedict equation (revised 1984) tends to overestimate BMR slightly. If you know your body fat percentage, the Katch-McArdle formula is the most accurate of all three.
The Katch-McArdle formula calculates BMR from lean body mass (weight minus fat mass) rather than total weight. It is the most accurate BMR formula when body fat percentage is known, making it ideal for athletes, bodybuilders, and muscular individuals whose BMI or total weight may not reflect their actual body composition.
Absolutely. Our BMR calculator runs entirely in your browser. Your age, weight, height, sex, and body fat percentage are never sent to any server or tracked in any way. Everything stays completely private on your device.
Yes — our BMR calculator is 100% free with no signup, no account, no premium tier, and no usage limits. Calculate your BMR as many times as you need, completely free forever.
The Mifflin-St Jeor equation is accurate to within ±10% for most people. Individual metabolism varies based on genetics, hormones, muscle mass, and other factors. Use your BMR result as a starting point, track your weight for 2–3 weeks, and adjust your calorie intake based on real results.
Yes. Your BMR is the minimum calories your body needs at rest. To lose weight, you need to eat below your TDEE (not below your BMR). Use the TDEE reference table in the results to find your maintenance calories, then create a deficit of 300–500 kcal/day for sustainable weight loss.
Yes — BMR decreases with age and changes with significant weight gain or loss. It is recommended to recalculate your BMR every 4–6 weeks during an active weight loss or muscle gain phase to keep your calorie targets accurate. Our BMR calculator makes this quick and easy.