BMR Calculator
Find out your Basal Metabolic Rate — the number of calories your body burns at rest.
BMR Calculator
Calculate your Basal Metabolic Rate instantly.
Your BMR
0A BMR calculator shows exactly how many calories your body burns while doing nothing at all, simply keeping your heart beating, your lungs breathing, and your cells functioning. Enter your age, gender, height, and weight, and Toolnix calculates your basal metabolic rate using both the modern Mifflin-St Jeor equation and the older Harris-Benedict formula, giving you a useful comparison between the two most widely referenced approaches in nutrition science.
What Basal Metabolic Rate Actually Measures
Basal metabolic rate represents the minimum energy your body requires to sustain essential functions while completely at rest, including breathing, circulation, cell repair, and maintaining body temperature. For most people, BMR accounts for somewhere between 60 and 75 percent of total daily calorie burn, meaning the majority of the calories you use each day come simply from existing, not from deliberate exercise or movement. This makes BMR the essential starting point for any accurate calorie planning.
How to Use This BMR Calculator
Enter your current age, select your gender, and input your height and weight using either metric or imperial units. Once calculated, you will see your BMR displayed using the Mifflin-St Jeor formula as the primary figure, with the Harris-Benedict result shown alongside for comparison. From there, multiplying your BMR by an activity factor gives you your total daily energy expenditure, which is the number most people actually use for calorie and diet planning.
Comparing the Mifflin-St Jeor and Harris-Benedict Formulas
Mifflin-St Jeor (Men): BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Mifflin-St Jeor (Women): BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Harris-Benedict (Men): BMR = 88.36 + 13.4 × weight(kg) + 4.8 × height(cm) − 5.7 × age
Harris-Benedict (Women): BMR = 447.6 + 9.2 × weight(kg) + 3.1 × height(cm) − 4.3 × age
Both formulas shown for comparison — Mifflin-St Jeor is considered more accurate for modern populations
The Mifflin-St Jeor equation was developed more recently and has been validated as more accurate across a broader range of modern body types compared to the Harris-Benedict formula, which dates back to 1919 and was later revised in 1984. Harris-Benedict is still shown here since some older clinical guidelines and calculators continue to reference it.
Why Muscle Mass Changes Your BMR
Muscle tissue is metabolically active, meaning it burns calories even at rest simply to maintain itself, while fat tissue burns comparatively little. This is why two people at an identical body weight can have noticeably different BMR results if one carries significantly more muscle mass than the other. It also explains why strength training tends to raise resting calorie burn over time, since building additional muscle increases your baseline metabolic demand even outside of workout sessions.
| Body Composition | Weight | BMR (Estimate) | Difference |
|---|---|---|---|
| High Muscle Mass | 80 kg | 1,850 cal/day | +350 cal |
| Average Muscle Mass | 80 kg | 1,650 cal/day | +150 cal |
| Low Muscle Mass | 80 kg | 1,500 cal/day | Baseline |
How BMR Connects to Your Overall Calorie Plan
Knowing your BMR on its own is useful, but it becomes genuinely actionable once you multiply it by an activity factor to find your total daily energy expenditure. From there, subtracting calories creates a deficit for weight loss, matching that figure maintains current weight, and adding calories supports muscle gain. This is why BMR functions as the foundation underneath nearly every calorie-based diet or nutrition plan, regardless of the specific goal someone is working toward.
📉 Weight Loss
TDEE − 500 calories = sustainable 1 lb/week loss
⚖️ Maintenance
TDEE = calories needed to maintain current weight
📈 Muscle Gain
TDEE + 300 to 500 calories = steady muscle growth
Pro Tip: Activity multipliers range from 1.2 (sedentary) to 1.9 (very active). Multiply your BMR by the appropriate factor to find your true TDEE.
Frequently Asked Questions
Most adults have a BMR somewhere between 1,200 and 2,000 calories per day, with the exact figure depending heavily on body size, muscle mass, age, and gender.
The Mifflin-St Jeor equation is generally considered more accurate for most healthy adults, since it was developed more recently and validated against a broader range of modern body compositions.
Yes, muscle tissue burns more calories at rest than fat tissue does, so a person with greater muscle mass will typically have a higher BMR than someone of the same weight with less muscle.
No, BMR only measures calories burned at complete rest, while TDEE adds your daily activity level on top of that baseline to reflect your full daily calorie burn.
Yes, BMR tends to decline gradually with age, largely due to a natural, gradual loss of muscle mass that often occurs unless it is actively countered with strength training.
Knowing your BMR separately helps you understand how much of your calorie burn comes from simply existing versus from activity, which is useful context if your activity level changes significantly.