BMR Calculator – Basal Metabolic Rate

Illustration of human metabolism and basal metabolic rate energy use

How Many Calories Does Your Body Burn at Rest?

Your body burns energy even when you do nothing

Even when you are doing absolutely nothing — lying in bed, reading this page — your body is burning calories. Your heart is beating, your lungs are working, your brain is running. The number of calories your body needs each day just to keep those vital systems running is your basal metabolic rate (BMR).

Knowing your BMR is the foundation of every calorie plan: weight loss, weight gain, and maintenance all start from this number. Enter your age, gender, height, and weight below and our free BMR calculator will estimate it in seconds using the Mifflin-St Jeor equation — the formula nutrition researchers consider most accurate for the general adult population.

yrs
ft in
lbs
–
calories per day (BMR)
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Sedentary (×1.2)
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Light exercise (×1.375)
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Moderate exercise (×1.55)
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Very active (×1.725)

Uses the Mifflin-St Jeor equation (1990), the most accurate BMR formula for most adults. BMR is your calories at complete rest — your actual daily need (TDEE) is higher once activity is added. Activity estimates above are starting points, not medical advice.

Healthy metabolism supported by balanced nutrition and active habits
BMR is the biggest slice of your daily energy use — usually 60–75% of all calories burned.

How to Use This BMR Calculator

  1. Pick your unit system. Choose US units (feet/inches, pounds) or Metric (centimeters, kilograms) at the top of the calculator.
  2. Select your gender. Men and women burn energy at different rates, so the formula adjusts automatically.
  3. Enter your age. BMR falls gradually as you get older — the formula accounts for that.
  4. Enter your height and weight. Use your morning weight for the most consistent readings.
  5. Hit Calculate. Your BMR appears instantly, along with a transparent breakdown of exactly how the number was built and your estimated daily calorie needs at four activity levels.

What Is BMR?

BMR stands for basal metabolic rate — the minimum number of calories your body needs in 24 hours to sustain basic life functions while completely at rest: breathing, circulation, cell repair, body temperature regulation, and brain activity. It typically accounts for 60–75% of the calories you burn each day, making it the single biggest piece of your total energy picture.

  • BMR is not the calories you “should eat.” It is your resting floor. Once you add walking, work, exercise, and even digestion, your real daily burn (called TDEE) is higher — usually 20–90% higher depending on activity.
  • It varies enormously between people. A young, tall, muscular man might have a BMR above 1,900 calories; a smaller, older woman might sit near 1,200. That gap is normal — it’s driven by body size, muscle mass, age, and sex.
  • You should not eat below your BMR for long. Consistently eating fewer calories than your body needs at rest can slow metabolism, drain energy, and backfire on weight-loss goals.

BMR is closely related to RMR (resting metabolic rate), but the two are measured under different conditions — RMR is taken in less strict lab settings and usually reads slightly higher.

BMR Formula (Mifflin-St Jeor) + Worked Example

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

The difference comes down to body composition: on average, men carry more muscle mass (which burns more energy at rest), hence the +5 versus −161 adjustment. This equation, published in 1990, has been validated as more accurate than the older 1918 Harris–Benedict formula for most adults.

Worked example: A 30-year-old woman who weighs 65 kg and is 165 cm tall. Weight component: 10 × 65 = 650. Height component: 6.25 × 165 = 1,031.25. Age component: 5 × 30 = 150. Gender adjustment (women): −161. BMR = 650 + 1,031.25 − 150 − 161 = about 1,370 calories per day at complete rest. Add moderate activity (×1.55) and her estimated total daily burn is about 2,124 calories.

Limitations of a BMR Calculator

A BMR calculator gives an estimate, not a lab measurement — and honest use means knowing where the edges are:

  • It’s an equation, not a scan. The true reference method is indirect calorimetry in a lab. Formula estimates are usually within about 10% for typical adults, but individual metabolism can differ.
  • It can’t see body composition. Two people with the same height, weight, age, and sex get the same number, even if one has far more muscle — and muscle burns more energy at rest than fat.
  • It doesn’t capture everything. Illness, medication (especially thyroid-related), pregnancy, and extreme dieting history can all shift real metabolic rate outside what the formula predicts.
  • Not designed for everyone. This tool gives estimates for adults (roughly ages 15–100). It is not designed for children, pregnant women, or people with medical conditions affecting metabolism — in those cases, a clinician’s assessment is the right path.

Use your BMR as a well-grounded starting point, then let your real-world weight trend over 2–3 weeks confirm or adjust it.

Tips for Using Your BMR Effectively

  • Weigh yourself in the morning. Weight fluctuates through the day; a consistent morning reading keeps your BMR estimate comparable over time.
  • Treat BMR as the floor, not the goal. Your actual daily need is higher — use the activity-level estimates in the result as your planning range.
  • Recalculate after big changes. Significant weight loss or gain, a new training routine, or a birthday milestone all shift your number.
  • Build muscle to nudge BMR upward. Muscle tissue burns more energy at rest than fat, so strength training is the most reliable long-term lever for a higher BMR.
  • Pair it with TDEE. BMR is half the story; total daily energy expenditure (BMR × your activity level) is what actually sets your calorie budget.
  • Don’t chase a “high BMR” number. A higher BMR is not automatically better — accuracy and consistency matter more than the raw figure.
Medical disclaimer: This tool is for informational purposes and is not medical advice. BMR calculators give estimates; consult a qualified healthcare professional before making health decisions.

Related Tools

TDEE Calculator

Your total daily energy expenditure — what resting calories become once your actual day is added in.

Calorie Calculator

Maintenance, weight-loss, and weight-gain targets built on your metabolic rate.

BMI Calculator

A quick snapshot of where your weight sits for your height, alongside your BMR.

BMR vs RMR: A Quick Distinction

BMR and RMR (resting metabolic rate) sound interchangeable, but they are measured differently. BMR is the strict version: taken after an overnight fast, lying completely still, in a temperature-neutral room, with no recent exercise. RMR relaxes those conditions — a shorter rest, less preparation — making it the practical choice for clinics and gyms, and it typically reads up to about 10% higher.

For planning, the gap rarely matters (10% of 1,600 calories is 160, inside any formula’s error). A better formula fit matters more. If you know your body fat percentage, the Katch-McArdle equation works from lean mass instead: BMR = 370 + (21.6 × lean body mass in kg). An 80 kg man at 20% body fat has 64 kg of lean mass, giving 1,752 calories — close to the 1,780 Mifflin-St Jeor gives a 30-year-old man of the same size (80 kg, 180 cm). Two independent methods landing within a couple of percent is a number you can plan around.

Frequently Asked Questions

What is BMR in simple terms?
BMR is the number of calories your body burns in a day just to stay alive while doing nothing — breathing, heartbeat, brain function, and body heat. Think of it as your body’s idle fuel consumption.
What is the difference between BMR and TDEE?
BMR covers only your resting energy needs. TDEE (total daily energy expenditure) adds everything else: daily movement, work, exercise, and digestion. TDEE is always higher than BMR — usually by 20–90% depending on how active you are.
Which BMR formula is the most accurate?
For most adults, the Mifflin-St Jeor equation is considered the most accurate widely available formula. The older Harris–Benedict equation (1918) tends to overestimate for many people.
Why is my BMR lower than the calories I eat?
Because BMR only covers you at rest. Once you add walking, working, exercising, and digesting food, your true daily burn is significantly higher — that is the number your eating should be compared against.
How can I increase my BMR?
The most reliable way is building muscle through strength training, since muscle burns more calories at rest than fat. Eating enough protein, staying active, getting enough sleep, and avoiding extreme crash diets all help.
Why do men and women get different BMR results?
The equations use different adjustments (+5 for men, −161 for women) because men, on average, carry more muscle mass and larger body frames, which require more resting energy. Individual results always vary with actual body composition.
What is the difference between BMR and RMR?
BMR is measured under strict conditions — fully rested, fasted overnight, in a neutral temperature. RMR is measured with looser preparation and typically reads up to about 10% higher. In everyday use the terms are nearly interchangeable, and calculators like this one estimate BMR.
What is a normal BMR?
Most adult women fall roughly between 1,200 and 1,800 calories per day, and most adult men between 1,600 and 2,400, driven mainly by body size, age, and muscle mass. A value outside those bands is not automatically a problem — very small or very large people naturally fall beyond them.

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