BMR Calculator
Ever wondered how many calories your body burns just staying alive? Not exercising, not eating, not doing anything at all — just existing. That number is your Basal Metabolic Rate, and it is way more interesting than you might think. Our BMR calculator uses the Mifflin-St Jeor equation, the gold standard formula endorsed by the Academy of Nutrition and Dietetics, to give you a personalized estimate in seconds. Pop in your age, gender, weight, and height, and you get two powerful numbers: your BMR (calories burned at complete rest) and your TDEE (total daily calories including all activity). Whether you are trying to lose fat, build muscle, maintain your current weight, or just understand your body better, knowing your BMR is the smartest starting point. No sign-ups, no email required, no data stored. Just instant, science-backed results you can actually use.
What Is
BMR stands for Basal Metabolic Rate — the minimum number of calories your body requires to keep you alive while you do absolutely nothing. We are talking about the energy needed to breathe, circulate blood, maintain body temperature, grow and repair cells, and keep every single organ functioning. Even lying in bed all day watching Netflix, your body is burning through calories just to keep the lights on. BMR typically accounts for 60 to 75 percent of your total daily calorie expenditure. The Mifflin-St Jeor equation, published in 1990, is currently considered the most accurate formula for predicting BMR in healthy adults. Here is how it works: for men, BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5. For women, BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161. The gender difference accounts for the fact that men tend to have more lean muscle mass and less body fat percentage at the same weight. At 70 kg, 175 cm, 30 years old, a mans BMR is approximately 1,648 calories, a womans about 1,482 calories. Your BMR is influenced by several factors beyond the formula: genetics can cause up to a 10 percent variation, muscle mass bumps it up (muscle burns more calories at rest than fat), and crash dieting can temporarily suppress it by as much as 15 to 20 percent (the so-called starvation mode). Thyroid function also plays a major role — hyperthyroidism can raise BMR significantly, while hypothyroidism lowers it. After knowing your BMR, multiplying it by an activity factor (1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active, 1.725 for very active) gives you your TDEE — the real number to use for diet planning.
How to Use
- Select your gender. This matters because the Mifflin-St Jeor equation uses different constants for men and women due to differences in average body composition and hormonal profiles.
- Enter your current age in years. BMR naturally declines with age — roughly 1 to 2 percent per decade after age 20 — as muscle mass tends to decrease and fat mass increases.
- Enter your current weight in kilograms or pounds. Use your most accurate measurement, ideally taken in the morning after using the bathroom and before eating or drinking anything.
- Enter your height in centimeters or feet/inches. Posture and time of day can slightly affect height measurement, so stand straight against a wall for the most accurate reading.
- Click the Calculate button. Your results display your estimated BMR in calories per day (kcal/day) using the Mifflin-St Jeor equation along with a confidence note.
- Review your TDEE at each activity level. The calculator shows projected daily calorie expenditures for sedentary, lightly active, moderately active, and very active lifestyles.
- Use these calorie numbers to plan your nutrition. For weight loss, aim for a deficit of 300 to 500 calories below your TDEE. For muscle gain, eat 200 to 300 calories above it.
Examples
Input: Male: 75kg, 175cm, 30yo
Process: BMR=1699 kcal/day
Result: BMR=1699 kcal/day (resting metabolism)
Input: Female: 60kg, 162cm, 25yo
Process: BMR=1327 kcal/day
Result: BMR=1327 kcal/day (resting metabolism)
Input: Male: 85kg, 180cm, 45yo
Process: BMR=1755 kcal/day
Result: BMR=1755 kcal/day (resting metabolism)
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Frequently Asked Questions
What is a normal BMR range?
For most healthy adult women, BMR falls between 1,200 and 1,600 calories per day, while adult men typically range from 1,500 to 1,900 calories per day. However, normal varies significantly based on body size, muscle mass, age, and genetics. A 5-foot-4-inch, 130-pound woman will have a much lower BMR than a 6-foot-2-inch, 200-pound man. Rather than comparing your number to a chart, the most useful approach is to track your personal BMR over time and see how it changes as you gain muscle, lose fat, or age. A BMR that increases over months is usually a sign you have built metabolically active muscle tissue.
How accurate is the Mifflin-St Jeor equation?
In validation studies, the Mifflin-St Jeor equation predicts BMR within approximately 10 percent of measured values for most healthy non-obese adults. That means if your calculated BMR is 1,500 calories, your actual BMR likely falls somewhere between 1,350 and 1,650 calories. It is more accurate than the older Harris-Benedict equation, especially for people who are overweight or obese. For clinical or competition-level precision, indirect calorimetry (a breathing test performed in a lab) remains the gold standard.
Can I increase my BMR?
Yes, though the changes are usually gradual. The most effective strategy is building muscle through resistance training, since each pound of muscle burns about 6 to 7 calories per day at rest compared to roughly 2 calories per pound of fat. High-intensity interval training can elevate your metabolic rate for up to 24 hours after exercise. Eating adequate protein gives you a slight metabolic boost via the thermic effect of food (protein costs 20 to 30 percent of its calories to digest, versus 5 to 10 percent for carbs and 0 to 3 percent for fats). Staying hydrated, getting quality sleep, and avoiding prolonged crash diets also help keep your metabolism humming.
Why is my BMR lower than I expected?
A lower-than-expected BMR usually comes down to smaller body size, being female (due to typically higher body fat percentage), older age, low muscle mass, or an extremely low-calorie diet. When you slash calories drastically for extended periods, your body adapts by lowering BMR to conserve energy — this is called adaptive thermogenesis or metabolic adaptation. Other potential causes include underactive thyroid (hypothyroidism), certain medications, and consistent sleep deprivation. If you suspect your metabolism is abnormally slow, a blood test checking thyroid function is a good starting point with your doctor.
Should I eat at my BMR or my TDEE?
This depends on your goal. If you want to lose weight, eating below your TDEE but above your BMR is the safer long-term strategy — typically a 300 to 500 calorie deficit below TDEE. Dropping all the way to BMR or below risks muscle loss, nutrient deficiencies, and metabolic adaptation. If you are maintaining weight, eat at your TDEE. If you are trying to gain muscle, eat 200 to 500 calories above TDEE while progressively training. Eating at exactly your BMR is essentially sedentary-level fueling and is only appropriate for people on strict rest.