BMR Calculator

What Is a BMR Calculator?

A BMR calculator is a free health tool that estimates your Basal Metabolic Rate�the number of calories your body burns at rest just to keep your heart beating, lungs breathing, and cells functioning. This BMR calculator uses the scientifically validated Mifflin-St Jeor equation combined with your age, height, weight, and sex to calculate how many calories you need daily just to survive. It then multiplies that BMR by an activity factor to show your Total Daily Energy Expenditure (TDEE), which is how many calories you actually need to maintain your current weight�essential information for anyone tracking calories, losing weight, or building muscle. To understand how your BMI relates to these calorie needs, also try our free BMI calculator.

How to Use This BMR Calculator

1. Choose your unit system: Select US Units (pounds, feet/inches) or Metric Units (kilograms, centimeters).
2. Enter your demographics: Select your sex, enter your age, height, and current weight.
3. Set your activity level: Choose from sedentary, lightly active, moderately active, very active, or extremely active to reflect your typical weekly exercise and lifestyle.
4. View your BMR instantly: The calculator shows your Basal Metabolic Rate�calories burned at complete rest.
5. See your daily calorie needs (TDEE): Your BMR multiplied by the activity factor shows how many calories you need daily to maintain your weight.
6. Use this for planning: Eat below this number to lose weight (~500 calories/day for 1 pound/week loss), at this number to maintain, or above it to gain.

Key Features of This BMR Calculator

• Uses the Mifflin-St Jeor equation�the gold standard recommended by dietitians worldwide
• Accounts for age, sex, height, weight, and activity level for personalized results
• Shows both BMR (resting) and TDEE (daily needs) instantly
• Supports both US and metric units for international use
• Provides clear activity level categories matching real lifestyle patterns
• Useful for weight loss planning, muscle gain, or calorie tracking
• Completely private�calculations run in your browser, no data is sent anywhere
• Free and no signup required

Real-World BMR Calculator Scenarios

Scenario 1: Weight Loss Planning
A 35-year-old woman, 5'5", 180 lbs, lightly active (exercises 1-3 days/week). This BMR calculator shows her BMR is 1,500 calories/day, and her TDEE is roughly 1,800 calories. To lose about 1 pound per week, she'd aim for 1,300 calories/day�a moderate deficit that feels sustainable without extreme restriction. For complementary nutrition insights, try our free calories burned calculator to see how exercise impacts her total calorie expenditure.

Scenario 2: Understanding Why You're Not Losing
A 45-year-old man, 5'10", 200 lbs, sedentary (desk job). This BMR calculator shows his TDEE is only 2,100 calories/day because he doesn't exercise. He thinks he's "eating nothing" at 2,000 calories, but that's nearly his entire TDEE�leaving almost no deficit for weight loss. The insight: he either needs to cut calories further or increase activity.

Scenario 3: Muscle Gain and Calorie Surplus
A 28-year-old male lifter, 6'0", 185 lbs, very active (5-6 days/week training). This BMR calculator shows a TDEE of roughly 2,900 calories. To gain muscle at a controlled rate (~0.5 lbs/week), he'd aim for 3,200-3,400 calories/day�enough to fuel muscle growth without excessive fat gain.

What is BMR?

Your Basal Metabolic Rate (BMR) is the number of calories your body needs just to maintain basic functions�breathing, circulation, cell repair, and keeping your organs running while completely at rest, not digesting food or moving at all. For most people, BMR accounts for 60-75% of total daily calorie burn, which is why it's the foundation for any effective calorie or weight-management plan. Use our free calorie calculator to estimate your total daily calorie needs based on your activity level.

Why Mifflin-St Jeor instead of Harris-Benedict?

This calculator uses the Mifflin-St Jeor equation: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, plus 5 for men or −161 for women. It replaced the older Harris-Benedict equation, first published in 1919 and revised in 1984, after researchers in 1990 found Mifflin-St Jeor predicted resting metabolic rate more accurately for the modern population, likely because average body composition and lifestyles had shifted since 1919. It's now the formula most commonly recommended by dietitians and used in clinical nutrition settings.

BMR vs. TDEE

BMR only covers calories burned at rest, doing nothing. Your Total Daily Energy Expenditure (TDEE) adds in calories burned through daily activity, exercise, and even fidgeting, which is why this calculator multiplies your BMR by an activity factor (from 1.2 for sedentary up to 1.9 for extremely active) to estimate how many calories you actually need each day to maintain your current weight.

What this number can't tell you

Like any formula based on height, weight, age, and sex, this is a population-based estimate, not a lab measurement. Genetics, muscle mass, thyroid function, and certain medications can shift someone's actual resting metabolism up or down from the predicted number. This tool provides a general estimate, not medical advice talk to a doctor or registered dietitian for guidance specific to your body and health history. To better understand your overall health metrics and body composition alongside your BMR, also try our free body fat calculator to see how much of your weight is fat versus lean muscle.

FAQ

Should I eat exactly my TDEE?
Eating around your TDEE tends to maintain your current weight. Eating below it typically leads to weight loss, and eating above it to weight gain always consult a healthcare provider before making major dietary changes.

How accurate is this?
The Mifflin-St Jeor equation is considered one of the more accurate BMR formulas for the general population, but it's still an estimate individual metabolism can vary based on genetics, muscle mass, hormones, and other factors.

What's the difference between this and the Calorie Calculator?
This page focuses on BMR, your resting energy need. Our Calorie Calculator uses the same underlying formula but also shows suggested calorie targets for losing or gaining about one pound per week.

Why do men and women get different results at the same height and weight?
The Mifflin-St Jeor equation adds a fixed adjustment based on sex because men typically carry more lean muscle mass at the same height and weight, and muscle burns more calories at rest than fat tissue does.

Does BMR change over time?
Yes. BMR generally declines with age as muscle mass naturally decreases, and it changes with significant weight loss or gain, which is why it's worth recalculating periodically rather than treating one result as permanent.

Is this medical advice?
No. This is a general estimate for informational purposes. Anyone with a medical condition, or planning a significant change in diet, should talk to a doctor or registered dietitian first.