BMR Calculator — Find Your Basal Metabolic Rate
Calculate your BMR using two industry-standard formulas and discover the minimum calories your body needs to survive each day.
Calculate Your BMR
Your BMR Results — Two Formulas Compared
Mifflin-St Jeor
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cal/day
More accurate — recommended for most people
Harris-Benedict
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cal/day
Original formula from 1919, revised 1984
Estimated TDEE at Moderate Activity
Mifflin-St Jeor × 1.55
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Harris-Benedict × 1.55
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For a precise TDEE, use the TDEE Calculator with your exact activity level.
What is BMR?
Basal Metabolic Rate (BMR) is the number of calories your body needs to perform its most basic, life-sustaining functions — breathing, circulation, cell production, protein synthesis, and temperature regulation — while at complete rest. It represents the minimum energy required to keep you alive.
BMR accounts for roughly 60-70% of your total daily calorie expenditure, making it the largest component of your energy needs by far. Even if you did nothing but lie in bed all day, your body would still burn your BMR worth of calories.
Understanding your BMR is the foundation of any effective nutrition plan because it tells you the absolute floor below which you should never eat — eating fewer calories than your BMR for extended periods causes muscle loss, hormonal disruption, and metabolic damage.
BMR vs. TDEE
BMR and TDEE are related but distinct measurements. Your BMR is a theoretical baseline — it assumes zero activity, zero food digestion, and a perfectly controlled environment. Nobody actually burns only their BMR in real life.
TDEE (Total Daily Energy Expenditure) takes your BMR and multiplies it by an activity factor to account for everything you actually do: walking, typing, exercising, even digesting your food (the thermic effect of food adds about 10% to energy needs).
The Relationship:
BMR × Activity Multiplier = TDEE
For most people, TDEE is 20-90% higher than BMR. A sedentary person's TDEE is about 1.2× their BMR, while an extremely active person's TDEE can be nearly 2× their BMR.
Which Formula is More Accurate?
Both formulas estimate BMR, but research shows the Mifflin-St Jeor equation is the more accurate of the two for most modern individuals.
Mifflin-St Jeor (1990)
Developed in 1990 using data from a more diverse modern population. Multiple studies have validated it as the most accurate formula for predicting resting energy expenditure in non-obese adults, with an error rate of about ±10%.
Male: (10×kg) + (6.25×cm) − (5×age) + 5
Female: (10×kg) + (6.25×cm) − (5×age) − 161
Harris-Benedict (1919, revised 1984)
The original BMR formula, first published in 1919 and revised by Roza and Shizgal in 1984. It was developed using a smaller and less diverse dataset. It tends to overestimate BMR by 5-15% compared to actual measured metabolic rates in modern populations.
Male: 88.362 + (13.397×kg) + (4.799×cm) − (5.677×age)
Female: 447.593 + (9.247×kg) + (3.098×cm) − (4.330×age)
Factors That Affect Your BMR
Muscle Mass
Skeletal muscle is metabolically active tissue — it burns approximately 6 calories per pound per day at rest, compared to fat tissue which burns only about 2 calories per pound. Building more muscle is one of the most effective long-term strategies for raising your BMR, which is why strength training is superior to cardio for sustainable fat loss.
Age
BMR naturally declines with age — approximately 1-2% per decade after age 20. This happens primarily because people tend to lose muscle mass as they age (sarcopenia), not because metabolism mysteriously slows down. People who maintain muscle mass through resistance training experience much smaller age-related drops in BMR.
Sex
Males typically have higher BMRs than females of the same height, weight, and age. This is primarily due to differences in body composition — males tend to carry more muscle mass and less body fat as a percentage of total body weight. Testosterone also plays a role in maintaining muscle mass and metabolic rate.
Genetics & Hormones
Thyroid hormones (T3 and T4) are the primary regulators of metabolic rate. Hypothyroidism can reduce BMR by 20-40%, while hyperthyroidism can increase it significantly. Genetic variation accounts for an estimated 40-70% of individual differences in BMR after controlling for body composition.
Related Calculators
TDEE Calculator
Multiply your BMR by your activity level to get your real daily calorie burn.
Try it →Macro Calculator
Use your BMR as the base to calculate your protein, carb, and fat targets.
Try it →Calorie Deficit Calculator
Find out how many calories to eat below your TDEE to reach your goal weight.
Try it →Frequently Asked Questions
For adult men of average height and weight (around 5'10", 185 lbs), a typical BMR ranges from 1,800-2,000 calories. For adult women of average stats (around 5'5", 145 lbs), a typical BMR is 1,400-1,600 calories. Taller, heavier, and more muscular individuals will have higher BMRs, while shorter, lighter individuals will have lower ones. These numbers can vary by hundreds of calories based on individual body composition.
No — eating below your BMR is generally not recommended and can be dangerous. Your BMR represents the calories needed for basic organ function. Consistently eating below BMR causes your body to break down muscle tissue for energy, disrupts hormones (particularly thyroid and sex hormones), slows metabolism, causes nutrient deficiencies, and makes the diet unsustainable. For safe fat loss, create a deficit from your TDEE, not your BMR. Most professionals recommend never going below 1,200 calories for women or 1,500 calories for men.
Yes. The most effective way to increase BMR is to build more muscle through progressive resistance training. Since muscle tissue burns roughly 3× more calories at rest than fat tissue, adding even 5-10 lbs of muscle can meaningfully raise your BMR. Eating enough protein (0.8-1.0g per lb of body weight) supports muscle retention and growth. Avoiding very low calorie diets protects against metabolic adaptation. Adequate sleep (7-9 hours) is also important — sleep deprivation measurably reduces metabolic rate.
Formula-based BMR calculators are estimates with an inherent error range of approximately ±10-15%. For most people this means the calculated BMR is within 150-250 calories of the actual measured value. The gold standard for measuring true BMR is indirect calorimetry — a clinical test done in a lab while fasting and completely at rest. For practical nutrition purposes, calculated BMR is accurate enough to serve as a reliable starting point, especially when combined with real-world tracking to fine-tune intake.
Yes — this is called metabolic adaptation or adaptive thermogenesis. When you consistently eat in a calorie deficit, your body responds by reducing its metabolic rate beyond what would be predicted from weight loss alone. Research shows that after significant weight loss, BMR can be suppressed by 10-15% below what the formula would predict for someone of that body weight. This is one reason why weight loss plateaus occur and why periodic "diet breaks" at maintenance calories can be beneficial during extended cuts.