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Fitness Calculators Tool

BMR Calculator

Determine your Basal Metabolic Rate (BMR) to find out how many calories your body burns at complete rest using Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle equations.

Educational & Scientific Tool: Outputs are estimated using validated physiological formulas for educational screening purposes. This tool is not a substitute for clinical medical evaluation, diagnosis, or personalized medical advice. See full Medical Disclaimer.

Parameters

years
cm
kg
%
Calculated Results

Formula & Math

How this calculation works under the hood:

Mifflin-St Jeor: BMR = 10 * Weight (kg) + 6.25 * Height (cm) - 5 * Age (years) + s (where s = +5 for males, -161 for females). Harris-Benedict (Revised): BMR = 13.397 * Weight (kg) + 4.799 * Height (cm) - 5.677 * Age (years) + 88.362 (males) OR 9.247 * Weight (kg) + 3.098 * Height (cm) - 4.330 * Age (years) + 447.593 (females). Katch-McArdle: BMR = 370 + 21.6 * LBM (Lean Body Mass in kg).

Worked Example

Real-world scenario walk-through:

For a 25-year-old male, 175 cm tall, weighing 70 kg (15% body fat): - Mifflin-St Jeor: 10*70 + 6.25*175 - 5*25 + 5 = 1,674 kcal/day - Revised Harris-Benedict: 88.362 + 13.397*70 + 4.799*175 - 5.677*25 = 1,724 kcal/day - Katch-McArdle (Lean Mass = 59.5 kg): 370 + 21.6 * 59.5 = 1,655 kcal/day.

Calculation Architecture

Every calculator follows the same four-stage pattern: normalize the inputs, apply the selected formula, compute supporting values, and classify the result against a practical benchmark.

  1. 1. Normalize units and defaults Convert metric and imperial values into a consistent calculation base and apply the configured default values if a field is untouched.
  2. 2. Select the best formula Many tools expose several scientific models so you can compare outputs instead of relying on one narrow estimate.
  3. 3. Compute supporting metrics Secondary outputs such as categories, healthy ranges, or maintenance targets make the result easier to apply in real life.
  4. 4. Interpret the number Use the result as a decision aid, then compare it with the reference ranges and FAQs below for context.

Input Reference

Input Default Bounds Role
Formula Type
Selection
 mifflin Method-dependent Chooses the method or activity tier.
Gender
Selection
 male Method-dependent Chooses the method or activity tier.
Age
Numeric field
 25 15 to 100 years Feeds the core formula and result classification.
Height
Numeric field
 175 / 69 100 to 250 cm / 39 to 98 inches Feeds the core formula and result classification.
Weight
Numeric field
 70 / 154 30 to 300 kg / 60 to 660 lbs Feeds the core formula and result classification.
Body Fat % (Katch-McArdle only)
Numeric field
 15 2 to 70 % Feeds the core formula and result classification.

Formula Breakdown

The calculator can expose one or more formula paths. When multiple equations are available, compare them to understand the spread in the estimate.

Mifflin-St Jeor
BMR = 10 * Weight (kg) + 6.25 * Height (cm) - 5 * Age (years) + s (where s = +5 for males, -161 for females).
Harris-Benedict (Revised)
BMR = 13.397 * Weight (kg) + 4.799 * Height (cm) - 5.677 * Age (years) + 88.362 (males) OR 9.247 * Weight (kg) + 3.098 * Height (cm) - 4.330 * Age (years) + 447.593 (females).
Katch-McArdle
BMR = 370 + 21.6 * LBM (Lean Body Mass in kg).

Worked Example

Step through the sample calculation line by line so the final answer is easy to audit.

  1. For a 25-year-old male, 175 cm tall, weighing 70 kg (15% body fat):
  2. Mifflin-St Jeor: 10*70 + 6.25*175 - 5*25 + 5 = 1,674 kcal/day
  3. Revised Harris-Benedict: 88.362 + 13.397*70 + 4.799*175 - 5.677*25 = 1,724 kcal/day
  4. Katch-McArdle (Lean Mass = 59.5 kg): 370 + 21.6 * 59.5 = 1,655 kcal/day.

Understanding BMR Calculator

Basal Metabolic Rate (BMR) represents the absolute baseline energy your body requires over 24 hours to perform essential survival processes—including cardiac contraction, pulmonary ventilation, cellular repair, renal filtration, and thermoregulation—while in a completely motionless, post-absorptive state.

Comparing Scientific BMR Formulas:

  • Mifflin-St Jeor: Endorsed by the Academy of Nutrition and Dietetics as the most accurate clinical formula for the general population, predicting resting metabolism within 10% of indirect calorimetry measurements for over 82% of subjects.
  • Revised Harris-Benedict: Updated by Roza & Shizgal in 1984 to eliminate historical bias, making it a reliable standard for non-obese individuals.
  • Katch-McArdle: Scaled directly to Lean Body Mass (LBM) rather than total weight. It is the premier choice for lean or heavily muscled athletes because skeletal muscle tissue expends significantly more baseline energy than adipose tissue.

Applying Your BMR Result: Never consume calories below your BMR without direct medical supervision. Chronically eating below BMR can trigger metabolic adaptation, thyroid hormone downregulation, loss of lean tissue, and systemic fatigue. Use your BMR as the anchor to calculate your Total Daily Energy Expenditure (TDEE).

How to use the fitness result

Fitness calculators work best when you track trends, not just single-day numbers. The goal is to turn the output into a training, nutrition, or body-composition decision.

  • Recheck after a meaningful training block or bodyweight change.
  • Use the result alongside performance, recovery, and waist or body-fat trends.
  • Compare multiple formulas when the calculator offers more than one estimate.

For this calculator in particular, use the output as a practical benchmark for training age, body composition, and benchmark comparisons. If the result looks off, check measurement technique first, then formula choice, then the unit mode.

As a rule, recalculate after a meaningful change in training load, diet, sleep, bodyweight, or performance. That keeps the number relevant without chasing noise.

Evidence-Based & Scientifically Verified
Updated: August 2026
ER
Written By
Dr. Elena Rostova, PhD
Lead Physiology & Exercise Science Contributor
MV
Reviewed By
Marcus Vance, CSCS, CPT
Senior Human Performance Reviewer
Sources reference peer-reviewed studies (PubMed, JISSN, WHO & ACSM clinical guidelines).

Scientific & Peer-Reviewed References

  • Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.
  • Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182.

FAQs

What is the difference between BMR and RMR? +

BMR (Basal Metabolic Rate) measures energy expenditure under strict laboratory conditions immediately upon waking after 12 hours of fasting. RMR (Resting Metabolic Rate) measures energy at rest without requiring strict overnight fasting, typically yielding numbers 5–10% higher than BMR.

Can I increase my BMR naturally? +

Yes. The most effective way to permanently raise your BMR is by increasing lean muscle mass through resistance training. Muscle tissue is metabolically active and requires continuous energy even during rest.

Why shouldn't I eat fewer calories than my BMR? +

Eating below your BMR deprives your body of energy needed to sustain basic organ functions. Prolonged severe restriction leads to muscle degradation, hormonal disruption, and metabolic slowing.

How often should I recalculate bmr? +

Recalculate whenever your bodyweight, training volume, recovery status, or goal changes enough to move the estimate. For most users, that means every 1 to 4 weeks depending on the calculator and the speed of change.

What should I do if this estimate seems too high or too low? +

Check your measurement inputs, confirm the unit mode, and compare the result against a second formula or a real-world trend. This is especially important for training age, body composition, and benchmark comparisons.

Should I compare this number to athlete standards or my own trendline? +

Use both. Athlete standards tell you where you sit relative to the population, while your own trendline shows whether your training, sleep, and nutrition are actually moving in the right direction.

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