BMR Calculator
Calculate your Basal Metabolic Rate (BMR) to understand how many calories your body burns at rest. Get personalized daily calorie needs based on your activity level.
BMR is the number of calories your body burns at complete rest. Most adults have a BMR between 1,200-2,000 calories per day.
Calculate your exact BMR and daily calorie needs below.
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Most accurate for modern populations
Classic formula (may overestimate)
Your Body Burns Calories While You Sleep, Here's How Many
Right now, as you're reading this, your body is burning calories. Not from exercise. Not from digesting food. Just from existing. Your heart's pumping blood, your lungs are pulling in oxygen, your brain's processing these words, and your cells are repairing themselves. All of that costs energy.
That baseline energy cost is your Basal Metabolic Rate, or BMR. Think of it like the fuel a car burns while idling in a parking lot. The engine's running, the air conditioning's on, the electronics are powered, but you're not going anywhere. That's BMR. It's the minimum your body needs just to keep the lights on.
And here's the part most people don't realise: BMR accounts for 60 to 75% of every calorie you burn in a day. Exercise? That's typically just 10 to 15%. So if you're trying to lose weight, build muscle, or just understand your body better, your BMR is the single most important number to know.
How Is BMR Calculated?
Scientists have developed several equations to estimate BMR from basic measurements, your weight, height, age, and sex. The two most widely used are the Mifflin-St Jeor equation (1990) and the Harris-Benedict equation (1919, revised 1984). Our calculator offers both.
Mifflin-St Jeor (recommended):
Men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
Women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161
Harris-Benedict (revised 1984):
Men: BMR = 88.362 + (13.397 x weight) + (4.799 x height) - (5.677 x age)
Women: BMR = 447.593 + (9.247 x weight) + (3.098 x height) - (4.330 x age)
Weight in kilograms, height in centimetres, age in years.
Which should you use? The Mifflin-St Jeor equation. A 2005 review by the American Dietetic Association tested both formulas against real metabolic measurements and found Mifflin-St Jeor predicted BMR within 10% of the actual value in more subjects than any other equation. Harris-Benedict tends to overestimate by 5 to 15%, especially in people who carry more body fat.
That said, both are estimates. The only way to measure your true BMR is indirect calorimetry, breathing into a machine that measures oxygen consumption and CO2 production. That costs $150 to $300 per test and is mostly used in clinical settings. For day-to-day planning, the Mifflin-St Jeor equation is accurate enough to build a solid nutrition plan around.
What Affects Your BMR?
Your BMR isn't fixed. It shifts based on several factors, some you can control, some you can't. Understanding what moves the needle helps you make smarter decisions about nutrition and training.
Muscle Mass
Muscle burns roughly 6 calories per pound per day at rest. Fat burns about 2. So a person with 150 lbs of lean mass has a naturally higher BMR than someone the same weight with less muscle. This is the #1 controllable factor.
Age
BMR drops about 1 to 2% per decade after your mid-20s. The main reason isn't age itself, it's the muscle loss (sarcopenia) that comes with being less active. People who strength train into their 60s and 70s maintain significantly higher metabolic rates.
Sex
Men typically have 10 to 15% higher BMR than women of the same size. This is largely due to higher testosterone levels, which promote greater muscle mass and lower essential fat stores.
Body Size
Larger bodies burn more energy at rest, more cells to maintain, more blood to circulate, more surface area losing heat. This is why BMR drops as you lose weight, and why calorie targets need periodic recalculation.
Genetics
Studies of identical twins show genetics account for about 40% of BMR variation. Some people genuinely run "hotter" than others. But this difference is typically 200 to 300 calories, not thousands.
Thyroid Function
Your thyroid gland produces hormones (T3 and T4) that directly regulate metabolic rate. Hypothyroidism can reduce BMR by 15 to 40%. If your calculated BMR seems far off from reality, a thyroid panel is worth requesting from your doctor.
What this means for you: If your weight loss has stalled or you feel like you "can't eat anything without gaining weight," the answer probably isn't a broken metabolism. It's more likely that your BMR has dropped because you've lost weight (smaller body = fewer calories needed) or lost muscle (less metabolically active tissue). The fix is recalculating your targets and prioritising strength training to rebuild lean mass.
Average BMR by Age and Sex
The table below shows estimated BMR values for average-weight adults at each age bracket. These are calculated using the Mifflin-St Jeor equation with reference body weights from the NHS.
| Age Range | Men (kcal/day) | Women (kcal/day) |
|---|---|---|
| 18 to 25 | 1,700 to 1,900 | 1,350 to 1,500 |
| 26 to 35 | 1,650 to 1,850 | 1,300 to 1,450 |
| 36 to 45 | 1,600 to 1,800 | 1,250 to 1,400 |
| 46 to 55 | 1,550 to 1,750 | 1,200 to 1,350 |
| 56 to 65 | 1,500 to 1,700 | 1,150 to 1,300 |
| 66 to 75 | 1,400 to 1,600 | 1,100 to 1,250 |
| 76+ | 1,300 to 1,500 | 1,050 to 1,200 |
What this means for you: These are population averages based on typical body sizes. Your individual BMR depends on your specific weight, height, and body composition. A 55-year-old man who weighs 200 lbs and lifts weights regularly will have a higher BMR than the average shown here. Use the calculator above to get your personalised number, these ranges are just for context.
BMR vs TDEE: Which Number Should You Use?
This is one of the most common points of confusion. Your BMR tells you what your body burns at absolute rest. But you don't spend all day lying motionless in a temperature-controlled room, you walk, cook, fidget, exercise, and digest food. All of that costs extra calories.
Your Total Daily Energy Expenditure (TDEE) is BMR plus all that additional activity. It's calculated by multiplying your BMR by an activity factor:
| Activity Level | Multiplier | Example |
|---|---|---|
| Sedentary | BMR x 1.2 | Desk job, no exercise |
| Lightly Active | BMR x 1.375 | Light exercise 1 to 3 days/week |
| Moderately Active | BMR x 1.55 | Moderate exercise 3 to 5 days/week |
| Very Active | BMR x 1.725 | Hard exercise 6 to 7 days/week |
| Extra Active | BMR x 1.9 | Athlete or very physical job |
The rule is simple: Use BMR to understand your metabolism. Use TDEE to plan your meals. If you eat at your TDEE, you'll maintain weight. Eat below it, you'll lose. Eat above it, you'll gain.
One critical warning: never eat below your BMR for extended periods. Your BMR represents the energy your organs need to function properly. Consistently undercutting it triggers metabolic adaptation, your body slows down non-essential processes like hormone production, immune function, and tissue repair to compensate. This makes fat loss harder, not easier.
5 Metabolism Myths That Won't Die
There's more bad advice about metabolism floating around the internet than almost any other health topic. Here's what the research actually says:
"Eating 6 small meals a day boosts your metabolism"
It doesn't. A 2010 study in the British Journal of Nutrition found no difference in metabolic rate between 3 and 6 meals per day when total calories were equal. The thermic effect of food (the energy cost of digestion) is the same whether you eat 2,000 calories in 3 meals or 6. Eat whatever meal frequency suits your lifestyle.
"My metabolism is 'broken', that's why I can't lose weight"
True metabolic disorders (like hypothyroidism) affect roughly 5% of the population and typically account for 5 to 10 lbs of weight gain, not 50+. For most people, the issue isn't a broken metabolism, it's that calorie intake is higher than they think, or their BMR has decreased because they've lost weight and lean mass. Recalculate, adjust, and focus on strength training.
"Eating late at night slows your metabolism"
Your body doesn't have a calorie curfew. A study published in Obesity found no difference in weight loss between early and late eaters when calories were controlled. What does matter: people who eat late tend to eat more, often snacking mindlessly in front of screens. It's the extra calories, not the timing.
"Certain foods 'speed up' your metabolism"
Green tea, cayenne pepper, and coffee do have a tiny thermogenic effect, but we're talking 30 to 80 extra calories per day. That's half a banana. You can't out-supplement a bad diet. The most effective metabolic booster is muscle mass, which burns calories 24/7.
"Starvation mode makes you gain weight"
Metabolic adaptation is real, your BMR does slow when you eat very little for a long time. But it doesn't make you gain weight from 1,000 calories. What happens is your weight loss slows or stalls because your body is burning fewer calories than predicted. The fix isn't eating even less, it's eating more (especially protein), adding resistance training, and taking periodic diet breaks.
How to Increase Your BMR (Evidence-Based)
You can't change your age, sex, or genetics. But you can change your body composition, and that's the biggest lever you have. Here's what works:
1. Build Muscle
Every pound of muscle you gain adds roughly 6 calories/day to your BMR. That sounds small, but 10 lbs of muscle adds 60 cal/day, which is 21,900 cal/year, roughly 6 lbs of fat. Compound lifts (squats, deadlifts, bench press, rows) 3 to 4 times a week is the most efficient path. Use our One Rep Max Calculator to program your training.
2. Eat Enough Protein
Protein has the highest thermic effect of any macronutrient, your body burns 20 to 30% of protein calories just digesting it (compared to 5 to 10% for carbs and 0 to 3% for fat). Aim for 0.7 to 1g per pound of body weight. Check our Protein Intake Calculator for your target.
3. Don't Crash Diet
Severe calorie restriction (under 1,200 cal/day for women, 1,500 for men) triggers metabolic adaptation. Your body downregulates thyroid hormones, reduces NEAT (fidgeting, walking, etc.), and sacrifices muscle to conserve energy. Use our Weight Loss Calculator to find a sustainable deficit instead.
4. Sleep 7 to 9 Hours
Sleep deprivation reduces BMR by 2.6% according to a study in the European Journal of Clinical Nutrition. Worse, it increases cortisol and ghrelin (hunger hormone) while decreasing leptin (satiety hormone), a perfect storm for overeating. Good sleep isn't a luxury; it's a metabolic requirement.
What this means for you: The most effective long-term strategy for a higher BMR is to build and maintain muscle. Everything else, protein, sleep, avoiding crash diets, supports that primary goal. If you only do one thing, make it strength training.
BMR in Action: A Worked Example
Let's make this concrete. Say you're a 35-year-old woman, 5'6" (167.6 cm), weighing 155 lbs (70.3 kg). Using the Mifflin-St Jeor equation:
BMR = (10 x 70.3) + (6.25 x 167.6) - (5 x 35) - 161
BMR = 703 + 1,047.5 - 175 - 161
BMR = 1,415 calories/day
This means your body needs about 1,415 calories just to keep your organs running. Now, if you exercise moderately (3 to 5 days/week), your TDEE would be:
TDEE = 1,415 x 1.55 = 2,193 calories/day
So to maintain your current weight, you'd eat around 2,200 calories. For gradual fat loss (0.5 kg/week), you'd subtract 500 calories:
Fat loss target = 2,193 - 500 = 1,693 calories/day
Notice how 1,693 is well above the BMR of 1,415. That's important. You're creating a deficit large enough for steady progress but not so large that your body panics and downregulates metabolism. This is the sustainable approach.
Where Do Your Calories Actually Go?
People assume exercise is the main calorie burner. It's not even close. Here's the actual breakdown of your daily energy expenditure:
| Component | % of Total | What It Is |
|---|---|---|
| BMR | 60 to 75% | Organ function, body temperature, cell repair, breathing, circulation |
| NEAT | 15 to 30% | Non-exercise activity: walking, cooking, fidgeting, typing, standing |
| TEF | 8 to 12% | Thermic effect of food, energy spent digesting, absorbing, and processing meals |
| Exercise | 5 to 15% | Planned workouts, running, lifting, swimming, cycling |
What this means for you: Exercise is brilliant for health, muscle building, and cardiovascular fitness. But for weight management, your BMR and NEAT are far more impactful. This is why people who exercise hard but sit at a desk for 10 hours often don't lose weight, the 400 calories they burned at the gym get eclipsed by 8 hours of near-zero NEAT.
The practical takeaway? Stay active throughout the day, take the stairs, walk during phone calls, stand at your desk. Small movements add up to 200 to 400 extra calories daily. Combine that with regular exercise and you've got a powerful one-two punch.
When to See a Doctor About Your Metabolism
Estimated BMR equations work well for most people. But certain signs suggest your actual metabolic rate might be significantly different from what the maths predicts:
- Unexplained weight gain or inability to lose weight despite consistently eating below your calculated TDEE for 6+ weeks, this could indicate hypothyroidism, which affects roughly 1 in 20 adults.
- Chronic fatigue, cold sensitivity, dry skin, or hair loss, classic signs of an underactive thyroid. A simple TSH blood test can confirm or rule this out.
- Unintentional weight loss despite eating normally, could indicate hyperthyroidism, where the thyroid produces too much hormone and drives BMR abnormally high.
- Extreme hunger with weight loss, may signal undiagnosed diabetes, where your body can't properly use glucose for energy.
- You're under 18 or over 75, BMR equations are calibrated for adults aged 18 to 75. Outside this range, individual variation increases and clinical assessment is more appropriate.
If any of these apply, a doctor can order a metabolic panel and thyroid function tests. A referral for indirect calorimetry (breathing test) can measure your true BMR to within 5% accuracy. Don't self-diagnose metabolic problems based on a calculator alone.
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How to use this tool
Select your preferred unit system (Imperial or Metric)
Enter your age and select your gender
Input your height and current weight
Common uses
- Finding your baseline calorie burn to plan a sustainable diet
- Understanding why weight loss has stalled despite eating less
- Comparing Mifflin-St Jeor and Harris-Benedict formula results
- Setting a calorie floor to avoid eating too little during a cut
- Calculating daily calorie needs by activity level for meal prep
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Frequently Asked Questions
What is BMR and why does it matter?
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How many calories does my body burn at rest?
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Why does BMR decrease with age?
Should I eat below my BMR to lose weight?
How often should I recalculate my BMR?
Why is my BMR different from my friend who weighs the same?
Does metabolism really slow down after 30?
What medical conditions affect BMR?
Results are for general informational purposes only and should be checked before use. They are not professional advice. See our Disclaimer and Terms of Service.