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BMR Calculator — Basal Metabolic Rate Calculator

Calculate your Basal Metabolic Rate using multiple formulas

BMR Calculator: Calculate Your Basal Metabolic Rate

Table of Contents - Bmr

How to Use This Calculator - Bmr

The calculator offers three formula options at the top: Mifflin-St Jeor (the default and most widely recommended), Harris-Benedict (the original BMR formula), and Katch-McArdle (which uses lean body mass and requires body fat percentage).

A unit toggle lets you switch between Metric (kg, cm) and Imperial (lbs, ft/in).

Enter your age, select your gender (male or female dropdown), and input your weight. For height in metric mode, enter centimeters in a single field. In imperial mode, enter feet and inches in separate fields.

If you selected the Katch-McArdle formula, an additional field appears for body fat percentage.

Click "Calculate BMR" to see your results. A "Clear" button resets all fields.

Results display your BMR in calories per day as a large number, along with a category label (like "Normal BMR") color-coded based on how your result compares to typical ranges. Below the main result, three boxes show your Daily, Weekly, and Monthly calorie needs based on BMR alone.

The Core Principle: Energy at Rest

Your Basal Metabolic Rate is the energy your body burns doing nothing at all—just existing. Breathing, circulating blood, maintaining body temperature, repairing cells, running your brain—these processes never stop and require constant fuel.

BMR typically accounts for 60-75% of your total daily energy expenditure. The rest comes from physical activity (exercise and non-exercise movement) and the thermic effect of food (energy used digesting and processing what you eat).

The variables that drive BMR are intuitive: larger bodies need more energy than smaller ones, so weight and height increase BMR. Muscle tissue burns more energy than fat tissue, so body composition affects BMR. Age brings gradual metabolic decline, so BMR decreases as you get older. Hormonal differences between males and females affect metabolism, so sex is a factor.

BMR is distinct from TDEE (Total Daily Energy Expenditure). BMR is the floor—the minimum energy you need. TDEE is BMR multiplied by an activity factor that accounts for movement and exercise.

How to Calculate BMR Manually

Mifflin-St Jeor Equation (most accurate for most people):

For men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5

For women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161

Example: 35-year-old woman, 65 kg, 165 cm BMR = (10 × 65) + (6.25 × 165) - (5 × 35) - 161 BMR = 650 + 1,031.25 - 175 - 161 = 1,345 calories/day

Harris-Benedict Equation (original formula):

For men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) - (5.677 × age)

For women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) - (4.330 × age)

Katch-McArdle Formula (uses lean body mass):

BMR = 370 + (21.6 × lean body mass in kg)

Lean body mass = weight × (1 - body fat percentage/100)

Example: 75 kg with 20% body fat Lean mass = 75 × (1 - 0.20) = 60 kg BMR = 370 + (21.6 × 60) = 370 + 1,296 = 1,666 calories/day

Converting BMR to TDEE (Activity Multipliers):

  • Sedentary (little/no exercise): BMR × 1.2
  • Lightly active (1-3 days/week): BMR × 1.375
  • Moderately active (3-5 days/week): BMR × 1.55
  • Very active (6-7 days/week): BMR × 1.725
  • Extremely active (twice daily/physical job): BMR × 1.9

Real-World Applications

Weight loss planning. To lose weight, you need to eat fewer calories than you burn. Knowing your BMR (then calculating TDEE) tells you how many calories to target. A typical recommendation: eat 500 calories below TDEE for approximately 1 pound of weight loss per week.

Weight gain planning. For gaining muscle, you need a caloric surplus. Knowing your baseline helps you determine how much extra to eat. A common approach: eat 250-500 calories above TDEE for lean muscle gain.

Maintenance calibration. If you're neither gaining nor losing weight, your current intake roughly equals your TDEE. Comparing this to your calculated TDEE helps validate (or question) the activity multiplier you chose.

Understanding plateau frustration. Your BMR decreases as you lose weight—there's less of you to maintain. A person who lost 30 pounds now has a lower BMR than before, which is why weight loss often stalls. Recalculating BMR after significant weight change helps reset expectations.

Medical and clinical applications. Healthcare providers use BMR estimates for nutritional planning, especially for patients who can't communicate their activity levels or who need precise nutritional support (hospitalized patients, eating disorder recovery, post-surgery nutrition).

Scenarios People Actually Run Into

The diet that stopped working. You've been eating 1,500 calories and losing weight, but progress has stalled. Your body adapted: as you lost weight, your BMR decreased, so the same 1,500 calories that created a deficit now only maintains your weight. Recalculate and adjust.

The activity overestimation trap. You selected "very active" because you exercise regularly, but you also have a desk job and sit most of the day. Your actual activity level is probably closer to "lightly active." Overestimating activity means eating more than your body burns, leading to unwanted weight gain.

The muscle mass advantage. Two people of identical height, weight, age, and sex can have different BMRs based on body composition. The person with more muscle burns more calories at rest. This is why strength training supports metabolic health.

The age factor reality check. At 25, your BMR might be 1,700 calories. At 45, everything else equal, it might be 1,600. At 65, it might be 1,500. The 5-calorie-per-year decline in the formula reflects real metabolic slowdown, mostly from muscle loss.

The formula disagreement. You calculate your BMR with Mifflin-St Jeor and get 1,450. Harris-Benedict gives you 1,520. Which is right? Both are estimates. The difference (about 5%) is within the margin of error for these formulas. Use either consistently.

Trade-Offs and Decisions People Underestimate

Formula accuracy limitations. These formulas are regression equations derived from population data. They estimate the average BMR for someone with your stats—but you might be above or below average. Individual variation can be 10-15%.

Lean mass advantage of Katch-McArdle. If you know your body fat percentage, Katch-McArdle is theoretically more accurate because it accounts for body composition. But body fat measurements have their own error margins, potentially offsetting the formula's advantage.

Activity multiplier selection. The multipliers are rough categories. "Moderately active" covers a wide range. Your actual multiplier might be 1.50 or 1.60, but you can only select one value. This is often where the biggest error enters TDEE calculations.

Metabolic adaptation. Extended calorie restriction can lower metabolic rate beyond what the formulas predict—your body "adapts" to conserve energy. This makes the formulas less accurate during and after prolonged dieting.

Health conditions affecting metabolism. Thyroid disorders, hormonal imbalances, and certain medications alter metabolic rate in ways the standard formulas can't capture. If your experience consistently doesn't match the calculations, consider medical evaluation.

Common Mistakes and How to Recover

Using BMR as eating target. BMR is not how much you should eat—it's the minimum for survival at complete rest. You need to eat more than BMR to fuel movement, exercise, and daily activities. Eating at BMR would create a severe deficit, leading to fatigue, muscle loss, and metabolic adaptation.

Forgetting to update after weight change. You calculated your TDEE at 200 pounds and stuck with that number as you dropped to 170. But your TDEE decreased along with your weight. Recalculate every 10-15 pounds lost (or gained).

Selecting the wrong units. You enter 70 in the weight field thinking kilograms, but the calculator is in imperial mode (interpreting it as 70 pounds). The result is wildly wrong. Verify units before calculating.

Ignoring the sex adjustment. The formulas differ significantly by sex due to typical body composition differences. Using the wrong formula adds or subtracts 150+ calories from the estimate.

Comparing BMR across formulas. You see your BMR is "1,450 with Mifflin-St Jeor" and worry because a friend's "1,600 with Harris-Benedict" is higher. Different formulas produce different numbers. Compare apples to apples.

Related Topics

Thermic Effect of Food (TEF). Digesting food requires energy—roughly 10% of caloric intake. Protein has the highest thermic effect (20-30%), followed by carbohydrates (5-10%), then fat (0-3%). This is one reason higher-protein diets can support weight loss.

Non-Exercise Activity Thermogenesis (NEAT). Fidgeting, walking, standing, typing—all the movement that isn't formal exercise. NEAT varies dramatically between people and can account for hundreds of calories per day. It's a hidden variable in the TDEE equation.

Resting Metabolic Rate (RMR). Similar to BMR but measured under less strict conditions. RMR is typically 10-20% higher than true BMR. Many "BMR calculators" actually estimate RMR. For practical purposes, the difference is minor.

Metabolic testing. Indirect calorimetry measures your actual metabolic rate by analyzing oxygen consumption and carbon dioxide production. More accurate than formulas but requires specialized equipment.

Set point theory. The hypothesis that your body defends a particular weight range by adjusting hunger, metabolism, and activity. This may explain why weight regain after dieting is common and why maintenance requires ongoing attention.

How This Calculator Works

The calculator accepts age, sex, weight, and height inputs. For imperial units, it converts feet/inches to centimeters and pounds to kilograms before applying the formulas.

Based on the formula selection, it applies the appropriate equation:

Mifflin-St Jeor uses the coefficients: (10 × weight) + (6.25 × height) - (5 × age), plus 5 for males or minus 161 for females.

Harris-Benedict uses different coefficients, with a base value and separate multipliers for weight, height, and age, varying by sex.

Katch-McArdle first calculates lean body mass (weight × (1 - body fat percentage/100)), then applies: 370 + (21.6 × lean mass).

The result is categorized based on typical BMR ranges: Very Low (below 1,200), Low (1,200-1,500), Normal (1,500-1,800), High (1,800-2,100), Very High (above 2,100). These ranges are rough guides—individual variation is significant.

Weekly and monthly values simply multiply the daily BMR by 7 and 30, respectively.

All calculations happen locally in your browser.

FAQs

What's the difference between BMR and TDEE?

BMR is calories burned at complete rest—just existing. TDEE (Total Daily Energy Expenditure) is BMR plus calories from activity and digestion. TDEE is what you'd eat to maintain weight; BMR is the floor you shouldn't go below.

Which formula is most accurate?

Mifflin-St Jeor is generally considered most accurate for the general population. Katch-McArdle may be more accurate if you have a reliable body fat percentage measurement. Harris-Benedict tends to slightly overestimate.

Should I eat at my BMR to lose weight?

No. Eating at BMR creates too severe a deficit for most people, leading to fatigue, muscle loss, and metabolic slowdown. Calculate your TDEE and eat 500-750 calories below that for sustainable weight loss.

Why does BMR decrease with age?

Mostly due to loss of muscle mass (sarcopenia). Muscle tissue is metabolically active; as it decreases, so does baseline energy expenditure. Strength training can partially counteract age-related BMR decline by preserving muscle.

Can I increase my BMR?

The most effective method is building muscle through resistance training. More muscle mass means higher BMR. Other factors—sleep quality, stress management, adequate protein—support metabolic health but have smaller effects than body composition.

How accurate are BMR formulas?

For most people, formulas estimate within 10-15% of actual measured BMR. Individual variation due to genetics, hormones, and health conditions can push actual BMR outside this range. Formulas are starting points, not precise measurements.

Does the Katch-McArdle formula require body fat percentage?

Yes. It calculates based on lean body mass, which requires knowing your body fat percentage. If you don't know this, use Mifflin-St Jeor instead.

How often should I recalculate my BMR?

After significant weight change (every 10-15 pounds) or annually if your weight is stable. As you age and your body changes, periodic recalculation keeps your nutrition targets appropriate.