What Is a BMR Calculator?
A BMR calculator estimates your basal metabolic rate — the calories your body burns every day just to stay alive, before you walk to the mailbox, lift weights, or digest lunch. Think of BMR as your metabolic floor: the baseline energy cost of breathing, pumping blood, regulating temperature, and repairing cells while you lie in bed. For anyone planning meals, cutting calories, or building muscle, knowing this number is the first step toward a realistic daily calorie target.
Our free BMR calculator applies the Mifflin-St Jeor equation, the formula most nutrition professionals prefer over older methods like Harris-Benedict because it tends to predict resting metabolism more accurately in modern populations. Enter your sex, age, height, and weight in imperial or metric units and you get an instant result in kilocalories per day. From there, multiply BMR by an activity factor to estimate total daily energy expenditure (TDEE) — or skip straight to our calorie calculator for maintenance, weight-loss, and weight-gain targets. For how we verify health formulas and source citations, see our editorial policy and methodology.
How to Use This BMR Calculator
- Choose imperial (lb, ft/in) or metric (kg, cm) units.
- Select your biological sex (male or female).
- Enter your age in years (15–120).
- Input your current height and body weight.
- Read your BMR in kcal/day — calories burned at complete rest.
- Use the copy button to save your result, then estimate TDEE with our calorie calculator or plan macros with our macro calculator.
How to Calculate BMR Manually (Mifflin-St Jeor)
The Mifflin-St Jeor equation was published in 1990 and validated against indirect calorimetry — the gold-standard lab method for measuring resting energy expenditure. Researchers found it predicted BMR within about 10% of measured values for most healthy adults, outperforming the revised Harris-Benedict equation in several comparison studies. That accuracy is why registered dietitians, sports nutritionists, and clinical guidelines often default to this formula when estimating resting metabolism.
The math is straightforward once your measurements are in metric units. Convert height to centimeters and weight to kilograms if you normally use feet, inches, and pounds. For men, multiply weight by 10, multiply height by 6.25, subtract five times your age, then add 5. For women, use the same weight, height, and age terms but subtract 161 instead of adding 5. The sex-specific constant accounts for average differences in lean body mass and hormonal influences on resting metabolism.
Here is a worked example. A 30-year-old man who is 5 feet 10 inches (178 cm) and weighs 180 pounds (about 82 kg) would calculate: BMR = (10 × 82) + (6.25 × 178) − (5 × 30) + 5 = 820 + 1,112.5 − 150 + 5 = 1,787.5 kcal/day, rounded to 1,788. A woman of the same age, height, and weight would subtract 161 instead of adding 5, yielding roughly 1,621 kcal/day — about 165 fewer calories at rest, reflecting typical sex differences in body composition.
BMR is only the starting point. Your actual daily burn includes non-exercise activity (NEAT), structured exercise, and the thermic effect of food. The National Institutes of Health Body Weight Planner and related nutrition guidance emphasize combining resting metabolic rate estimates with activity levels to set sustainable calorie targets — not relying on BMR alone. That is why we recommend pairing this tool with our TDEE calorie calculator and checking body composition context with our BMI calculator.
Mifflin-St Jeor BMR Formula
Men: BMR = 10W + 6.25H − 5A + 5
Women: BMR = 10W + 6.25H − 5A − 161
- W = Weight in kilograms (kg)
- H = Height in centimeters (cm)
- A = Age in years
Result is expressed in kilocalories per day (kcal/day), commonly called "calories" on food labels in the United States.
What Affects Your Basal Metabolic Rate?
Lean muscle tissue is metabolically active — it burns more calories at rest than fat tissue. That is why resistance training can nudge BMR upward over time even if scale weight stays flat. Age matters too: BMR typically drops 1–2% per decade after your twenties, largely due to gradual muscle loss unless you actively counter it with strength work and adequate protein. Genetics, thyroid function, sleep quality, and chronic stress also influence resting metabolism, which is why two people with identical height and weight can have slightly different measured BMR in a lab setting.
Formula-based estimates cannot capture every individual variation. Athletes with very low body fat, people recovering from illness, and those on certain medications may see results that diverge from prediction. Treat your calculated BMR as a well-supported estimate — then adjust based on real-world feedback. If you eat at your estimated maintenance calories for two to three weeks and weight stays stable, your TDEE estimate is on track. If you gain or lose unexpectedly, adjust intake by 100–200 kcal and reassess.
Frequently Asked Questions
What is BMR (basal metabolic rate)?▼
Basal metabolic rate (BMR) is the number of calories your body burns at complete rest to maintain vital functions such as breathing, circulation, and cell repair. It represents the minimum energy required to keep you alive and does not include calories burned through physical activity, digestion, or exercise.
How is BMR calculated?▼
This calculator uses the Mifflin-St Jeor equation (1990), which is widely recommended by dietitians and researchers. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(y) + 5. For women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(y) − 161. The result is expressed in kilocalories per day (kcal/day).
What is the difference between BMR and TDEE?▼
BMR measures calories burned at rest only. Total daily energy expenditure (TDEE) includes BMR plus all activity — walking, working, exercising, and even digesting food. To estimate how many calories you should eat daily, multiply BMR by an activity factor to get TDEE. Use our calorie calculator for a full TDEE estimate with weight goals.
Why is my BMR different from someone else's?▼
BMR varies based on sex, age, height, and weight. Men typically have higher BMR because they tend to carry more lean mass. BMR generally decreases with age as muscle mass declines. Taller and heavier individuals burn more calories at rest because their bodies require more energy to sustain a larger frame.
How can I use my BMR for weight loss or gain?▼
BMR alone is not your daily calorie target — you need TDEE for that. Once you know TDEE, eating below it promotes weight loss and eating above it promotes gain. A common approach is a 500 kcal/day deficit for roughly one pound of fat loss per week. Pair BMR with our calorie calculator and macro calculator to build a complete nutrition plan.