BMR Calculator | Calculate Your Basal Metabolic Rate

Q: What is the difference between BMR and TDEE?

BMR is the calories your body burns at complete rest, no movement, no digestion, no exercise. TDEE is BMR multiplied by an activity factor that accounts for all daily energy use including walking, exercise, and eating. For a sedentary adult, TDEE runs approximately 20 percent above BMR. For a very active person, TDEE runs 60 to 90 percent above BMR. Always use TDEE, not BMR, as the basis for your calorie target.

Q: What is the difference between BMR and RMR?

BMR is measured under strict laboratory conditions after a full night of sleep, 12 hours fasting, and zero movement. RMR (Resting Metabolic Rate) is measured under more relaxed conditions and typically runs 5 to 10 percent higher than true BMR. For practical calorie planning the difference is negligible. Most online calculators, including this one, return RMR-equivalent values using BMR formulas.

Q: Should I eat at my BMR to lose weight?

No. BMR is the calories your body needs at complete rest. The moment you stand, walk, or eat, your calorie burn already exceeds BMR. Eating at or below BMR creates an extreme deficit that accelerates muscle loss, fatigue, and metabolic adaptation. Set your calorie target a moderate amount below your TDEE, not below BMR, for sustainable fat loss that preserves lean mass.

Q: Which BMR formula is most accurate, Mifflin-St Jeor or Harris-Benedict?

Mifflin-St Jeor is more accurate for most healthy adults. A 2005 study in the Journal of the American Dietetic Association found Mifflin-St Jeor predicted resting metabolic rate within 10 percent for 82 percent of participants, outperforming Harris-Benedict. For lean athletes, the Katch-McArdle formula using lean body mass is even more precise, this calculator switches to it automatically when you enter body fat percentage.

Q: How does age affect BMR?

BMR declines approximately 1 to 2 percent per decade after age 20, primarily because skeletal muscle mass decreases by 3 to 5 percent per decade without resistance training. By age 60, the average person's BMR is roughly 10 to 20 percent lower than it was at 25. Regular strength training significantly slows this decline by preserving the lean mass that drives resting calorie burn.

Q: Can I permanently raise my BMR?

Yes, by building lean muscle mass through consistent resistance training. Each kilogram of muscle burns approximately 6 to 10 calories per day at rest, compared to roughly 2 calories for fat tissue. Adding 5 kilograms of lean mass raises your resting burn by 30 to 50 calories per day permanently. No supplement, food, or short-term protocol produces a comparable lasting effect.

Q: How often should I recalculate my BMR?

Recalculate every 4 to 6 weeks during an active fat loss or muscle gain phase, or any time your body weight shifts by more than 2 to 3 kilograms. BMR is calculated from your current weight and composition, so the number you started with becomes progressively less accurate as you progress. Recalculating and adjusting your calorie target is the single most common fix for fat loss stalls.

Use this free BMR calculator to find out exactly how many calories your body burns at rest each day. Enter your age, sex, weight, and height to calculate your Basal Metabolic Rate using the Mifflin-St Jeor formula. Add your body fat percentage to activate the Katch-McArdle formula and get a more precise result based on lean body mass.

Your Stats

Biological sex

Age

yrs

Weight

lbs

Height

Activity level (for TDEE estimate)

Body fat % (optional)

Know your body fat? Add it to switch to the Katch-McArdle formula — the most accurate option when lean mass is known.

Your results will appear here

Enter your stats to see your Basal Metabolic Rate.

What Is BMR? Understanding Basal Metabolic Rate

BMR, or Basal Metabolic Rate, is the total calories your body burns in 24 hours at complete rest, no movement, no digestion, no exercise. It is the minimum energy needed to keep your heart beating, lungs breathing, brain signaling, and cells repairing. For most adults, BMR makes up 60 to 70 percent of total daily calorie burn, making it the single largest and most important component of your energy expenditure.

This calculator uses the Mifflin-St Jeor equation, validated by the Academy of Nutrition and Dietetics as the most accurate predictive formula for resting energy expenditure in healthy adults. When body fat percentage is entered, it automatically switches to the Katch-McArdle formula, which uses lean body mass for a more precise result in lean or athletic individuals.

Organ Function & Circulation

Heart, lungs, kidneys, and liver account for ~70% of BMR despite being only ~5% of body weight, these organs run continuously around the clock.

Brain & Nervous System

The brain burns ~20% of resting calories despite being only 2% of body weight, consuming glucose constantly to maintain neural activity and signaling.

Thermoregulation

Your body spends significant energy maintaining a stable core temperature of 37°C regardless of external conditions, adding to baseline calorie expenditure hourly.

Cell Repair & Protein Synthesis

Every cell undergoes continuous maintenance, repair, and replacement. This biochemical housekeeping contributes meaningfully to resting calorie burn throughout every day.

How Does the BMR Calculator Calculate Your Basal Metabolic Rate?

The BMR calculator applies the Mifflin-St Jeor equation to your inputs and returns your resting calorie burn in three steps, with automatic formula switching based on whether you provide body fat percentage.

Stats
Formula
Result

Enter Your Stats

Enter your weight, height, age, and biological sex. Each variable shifts your BMR in a formula-defined way. Optionally add body fat percentage to activate the Katch-McArdle formula, which uses lean body mass instead of total weight for a more accurate result in lean or muscular individuals. Use the Body Fat Calculator if you need to estimate your percentage first.

What Factors Influence Your BMR and Basal Metabolic Rate?

Six biological and behavioral variables move BMR up or down. Understanding which ones you can actually control helps you focus on the levers that matter most.

Lean Muscle Mass

Muscle tissue burns 6–10 kcal per kilogram per day at rest, compared to roughly 2 kcal for fat tissue. This means that building muscle through consistent resistance training is the only reliable mechanism for permanently raising your BMR over months and years.

Age

BMR declines approximately 1–2% per decade after age 20, primarily because skeletal muscle mass falls by 3–5% per decade without resistance training. Consistent strength work is the single most effective counter to this age-related metabolic slowdown.

Body Size & Biological Sex

Larger bodies contain more cells and tissue to fuel, so BMR scales predictably with both weight and height. Men typically carry 10–20% more lean mass than women at equivalent body weights, which is why the Mifflin-St Jeor formula applies a sex-specific constant.

Genetics & Hormones

Thyroid hormone output, inherited metabolic rate, and life-stage hormones such as estrogen and testosterone all influence how many calories your body burns at rest. These factors explain why two people with identical age, weight, and height can differ by 200+ calories in daily BMR.

Climate & Core Temperature

Your body expends extra calories maintaining a stable core temperature of 37°C in cold environments, and fever raises BMR by roughly 7% for every degree Celsius of elevation. These thermoregulatory costs are real but rarely significant enough to affect everyday calorie planning.

Sleep & Recovery

Sleeping fewer than 6 hours per night reduces next-day resting metabolism and amplifies ghrelin, the hunger hormone. Prolonged aggressive caloric restriction compounds this by triggering adaptive thermogenesis, where the body actively lowers BMR to conserve energy.

How Do You Use BMR to Reach Your Goal?

BMR is your metabolic floor, the number every calorie strategy is built on top of. Here is what to do with it depending on your goal.

Lose Body Fat

Multiply your BMR by your activity factor to get TDEE, then eat 300–500 kcal below that number. Never eat at or below BMR, doing so triggers adaptive thermogenesis and accelerates muscle loss. Use the Calorie Deficit Calculator to set a safe, precise daily target.

Maintain Your Weight

Eating at your TDEE, your BMR multiplied by your activity level, holds your weight steady. BMR alone is not your maintenance number; it excludes all movement and digestion. Use the Maintenance Calorie Calculator to find your precise daily target with a verified 14-day tracking method.

Build Lean Muscle

Eat 200–300 kcal above your TDEE to fuel muscle repair and synthesis. Higher BMR follows as lean mass increases, each new kilogram of muscle adds ~6–10 kcal/day to resting burn permanently. Use the Macro Calculator to split the surplus into the right protein, carb, and fat targets.

What Are the Best Ways to Increase Your BMR?

Six evidence-based habits consistently raise BMR or prevent the metabolic slowdown that comes with dieting and aging.

1
Lift weights 2 to 4 times per week
to build lean muscle mass, the only proven mechanism for permanently raising resting metabolic rate over months and years
2
Hit 1.6 to 2.2 g of protein per kg of body weight daily
to protect muscle during a calorie deficit and support hypertrophy when training in a surplus
3
Avoid deficits larger than 500 kcal per day for extended periods
to prevent adaptive thermogenesis, where the body lowers BMR by 10 to 15 percent in response to prolonged severe restriction
4
Sleep 7 to 9 hours per night
to maintain thyroid function, regulate hunger hormones, and preserve next-day resting energy expenditure
5
Stay hydrated throughout the day
since even mild dehydration of 1 to 2 percent body weight can reduce resting metabolism measurably
6
Take a diet break every 8 to 12 weeks
by returning to maintenance calories for 1 to 2 weeks, allowing BMR to recover before the next deficit phase

Frequently Asked Questions About BMR

Quick answers to the questions people ask most.

What is a good BMR?

A good BMR depends on your body size, age, and sex. Adult men typically fall between 1,600 and 2,000 calories per day and adult women between 1,300 and 1,600. A higher BMR relative to your weight usually indicates more lean muscle mass. A lower BMR points to less muscle, lower body weight, older age, or prolonged caloric restriction causing metabolic adaptation.

What is the difference between BMR and TDEE?

What is the difference between BMR and RMR?

Should I eat at my BMR to lose weight?

Which BMR formula is most accurate, Mifflin-St Jeor or Harris-Benedict?

How does age affect BMR?

Can I permanently raise my BMR?

How often should I recalculate my BMR?