BMR Calculator
Calculate your Basal Metabolic Rate and daily calorie needs
What is Basal Metabolic Rate (BMR)?
Basal Metabolic Rate, or BMR, estimates how many calories your body would use at complete rest to keep essential functions running, including breathing, circulation, body temperature, cell repair, and basic organ activity. It is a starting point for understanding daily energy needs, because most total daily expenditure comes from resting metabolism before exercise or routine movement is added. This calculator uses common formulas and activity multipliers to estimate BMR and TDEE, which can help when planning weight loss, maintenance, or muscle gain. The result is still an estimate: body composition, sleep, medication, illness, hormones, training load, and tracking accuracy can all change real calorie needs.
How to Use
How to use
- Select your gender and calculation formula
- Choose unit system and enter your age, height, and weight (Katch-McArdle formula also requires body fat percentage)
- Click the calculate button to view your BMR result and daily calorie needs for different activity levels
Health Context
- BMR formulas estimate resting energy needs; activity level, muscle mass, illness, medication, and dieting history can change real needs.
- Use the number as a planning baseline, not a strict calorie prescription.
Use Cases
Technical Principle
Basal metabolic rate is estimated from one of three well-established equations: Mifflin-St Jeor (1990), the Roza-Shizgal revision of Harris-Benedict (1984, updated from the 1919 original), and Katch-McArdle. Mifflin-St Jeor is BMR = 10W + 6.25H - 5A + 5 for males and 10W + 6.25H - 5A - 161 for females, with weight in kilograms, height in centimeters, and age in years. The American Dietetic Association evidence review (2005) found Mifflin within +/-10% of indirect-calorimetry RMR for 82% of non-obese subjects and 70% of obese subjects, outperforming Harris-Benedict. Katch-McArdle bypasses sex and replaces total mass with lean body mass: BMR = 370 + 21.6 x LBM (kg), where LBM = weight x (1 - body-fat-fraction). Total daily energy expenditure is derived by multiplying BMR by a physical-activity level (PAL): 1.2 for sedentary office work, 1.375 for light exercise 1-3 days per week, 1.55 for moderate exercise 3-5 days, 1.725 for hard exercise 6-7 days, and 1.9 for an athlete or heavy physical occupation. These multipliers originate in WHO/FAO/UNU 2001 and Institute of Medicine 2002 dietary-reference-intake reports; they are population means with a documented inter-individual standard deviation of roughly 200-400 kcal per day at the same nominal PAL. Imperial inputs are converted to metric internally (1 lb = 0.45359237 kg, 1 in = 2.54 cm) before substitution into the equation, and the result is rounded to the nearest kilocalorie for display. Note the distinction between BMR and RMR: BMR is measured after 12 hours of fasting, 8 hours of sleep, and 30 minutes of supine rest in a thermoneutral chamber, while RMR drops the strict overnight-fast requirement and runs ~10% higher in practice. All three formulas approximate BMR/RMR for an average body composition; they will overestimate for very lean, muscular subjects and underestimate for sarcopenic-obese subjects, which is exactly the population where Katch-McArdle (driven by LBM) outperforms the others if a DEXA or BIA body-fat measurement is available.
- Mifflin-St Jeor: BMR = 10W + 6.25H - 5A +/- (5 male / -161 female), kcal/day.
- Katch-McArdle: 370 + 21.6 x LBM(kg); needs a body-fat % measurement to compute LBM.
- PAL multipliers from WHO/FAO/UNU 2001: 1.2 / 1.375 / 1.55 / 1.725 / 1.9.
- Mifflin-St Jeor is within +/-10% of calorimetry RMR for ~82% of non-obese adults (ADA 2005).
- Imperial-to-metric conversion uses 0.45359237 kg/lb and 2.54 cm/in before substituting into the formula.
- Adaptive thermogenesis can drop measured RMR by 5-15% during a sustained energy deficit; the formula does not model this.
- BMR is measured fasting and supine; RMR is the looser field equivalent and runs roughly 10% higher.
Examples
Male, 30 years, 75 kg, 175 cm (Mifflin-St Jeor)
Formula: 10 x weight + 6.25 x height - 5 x age + 5
BMR = 10 x 75 + 6.25 x 175 - 5 x 30 + 5
= 750 + 1093.75 - 150 + 5
= 1698.75 kcal/day
Moderately active (x 1.55) TDEE = approx 2633 kcal/dayFemale, 28 years, 60 kg, 165 cm (Mifflin-St Jeor)
Formula: 10 x weight + 6.25 x height - 5 x age - 161
BMR = 10 x 60 + 6.25 x 165 - 5 x 28 - 161
= 600 + 1031.25 - 140 - 161
= 1330.25 kcal/day
Lightly active (x 1.375) TDEE = approx 1829 kcal/dayHarris-Benedict vs Mifflin-St Jeor (same inputs)
Male, 35 years, 80 kg, 180 cm
Harris-Benedict: 88.362 + 13.397 x 80 + 4.799 x 180 - 5.677 x 35 = 1822 kcal
Mifflin-St Jeor: 10 x 80 + 6.25 x 180 - 5 x 35 + 5 = 1755 kcal
Difference: ~67 kcal/day - Mifflin tends to read lower for average builds.Katch-McArdle with 18% body fat
Lean mass = 75 kg x (1 - 0.18) = 61.5 kg
BMR = 370 + 21.6 x 61.5 = 370 + 1328.4 = 1698.4 kcal/day
Use this formula only when body fat is measured by DEXA, BIA, or skinfold.FAQ
What is BMR?
Basal Metabolic Rate is the calories your body burns at complete rest to keep core processes running - circulation, breathing, brain function, cell repair. It typically accounts for 60-70% of your total daily energy expenditure.
Which formula does this calculator use?
The Mifflin-St Jeor equation is the modern default: men BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; women BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. The page may also expose Harris-Benedict (older, slightly less accurate) and Katch-McArdle (uses lean body mass instead of weight).
How is TDEE calculated from BMR?
Total Daily Energy Expenditure = BMR × activity multiplier. Sedentary (desk job, no exercise) ≈ 1.2; light (1-3 sessions/week) ≈ 1.375; moderate (3-5/week) ≈ 1.55; heavy (6-7/week) ≈ 1.725; very heavy (manual labour or twice-daily training) ≈ 1.9. Most people overestimate their level by one tier.
Should I eat my BMR or my TDEE?
TDEE - BMR is what you burn doing literally nothing. To lose weight, eat below TDEE (a 300-500 kcal deficit is typical). To gain, eat above. Eating below BMR for long periods can drop your metabolism and is a common dieting mistake.
Why do men and women have different BMR formulas?
On average men carry more lean muscle and less fat at the same height/weight, and lean mass burns more calories at rest. Mifflin-St Jeor adds a +5/-161 sex term to capture that difference. If you have a body-composition reading, the Katch-McArdle formula (which uses lean body mass directly) is more individualised.
How accurate is the calculator?
Mifflin-St Jeor predicts BMR within roughly ±10% for most adults. Athletes, very lean or very obese people, older adults, and those with thyroid issues can deviate more. Track your weight over 2-3 weeks at a fixed intake and adjust calories rather than trusting the predicted number alone.
Is my data uploaded?
No. The calculation runs in your browser and inputs are not saved. Closing the page clears them.