Overview: What This Calculator Does
🔑 Key Points
- We use peer-reviewed scientific formulas published in medical journals
- All calculations are fully transparent — no proprietary algorithms
- Results are estimates with known accuracy ranges
- We clearly state limitations and when to seek professional guidance
Our TDEE (Total Daily Energy Expenditure) calculator estimates how many calories your body burns in a 24-hour period. It uses established mathematical formulas from published scientific research, taking your physical characteristics (age, biological sex, height, weight) and self-reported activity level to produce an estimate of your daily caloric needs.
Unlike many calculators that use undisclosed "proprietary formulas," we believe in complete transparency. On this page, you'll find the exact equations we use, their scientific origins, validation research, and honest discussion of their limitations.
Understanding TDEE & BMR
Before diving into formulas, it's important to understand what we're actually calculating and how your body uses energy.
What is BMR (Basal Metabolic Rate)?
BMR represents the minimum number of calories your body needs to perform essential life-sustaining functions while at complete rest in a thermoneutral environment. These functions include:
- Respiration: Breathing and oxygen exchange
- Circulation: Heart pumping blood throughout your body
- Cell Production: Creating new cells and repairing tissues
- Protein Synthesis: Building and maintaining muscle tissue
- Nutrient Processing: Basic metabolic processes in organs
- Brain Function: Neural activity (your brain uses ~20% of BMR)
- Temperature Regulation: Maintaining body temperature
BMR typically accounts for 60-75% of total daily calories burned, making it the largest component of your TDEE.
What is TDEE (Total Daily Energy Expenditure)?
TDEE is the total number of calories you burn in a day. It consists of several components:
BMR
Basal Metabolic Rate — calories burned at complete rest for basic survival functions
Physical Activity
Exercise + NEAT (Non-Exercise Activity Thermogenesis) — all movement from walking to workouts
TEF
Thermic Effect of Food — energy used to digest, absorb, and process nutrients
The Basic Calculation:
The activity multiplier accounts for both physical activity and TEF, which is why it's greater than 1.0 even for sedentary individuals (who still move somewhat and eat food).
The Scientific Formulas We Use
We offer three validated BMR equations, each with different strengths. All are from peer-reviewed scientific research and are widely used in clinical and research settings.
1. Mifflin-St Jeor Equation (1990)
Background
Developed by MD Mifflin, ST St Jeor, and colleagues at the University of Nevada, this equation was created from a study of 498 healthy individuals (247 women, 251 men) ranging from 19-78 years old with BMIs from 17-42 kg/m². The equation was designed to update older formulas and better reflect modern body compositions.
The Equations
BMR = (10 × weightkg) + (6.25 × heightcm) − (5 × ageyears) + 5BMR = (10 × weightkg) + (6.25 × heightcm) − (5 × ageyears) − 161Example Calculation
30-year-old male, 80kg, 180cm:
BMR = (10 × 80) + (6.25 × 180) − (5 × 30) + 5
BMR = 800 + 1125 − 150 + 5 = 1,780 calories/day
Why We Recommend It
A 2005 systematic review published in the Journal of the American Dietetic Association compared predictive equations and found the Mifflin-St Jeor equation was the most reliable, accurately predicting measured RMR within 10% for the highest percentage of individuals (82% of non-obese and 70% of obese subjects).
2. Harris-Benedict Equation (Revised 1984)
Background
The original Harris-Benedict equation was published in 1918 by James Arthur Harris and Francis Gano Benedict at the Carnegie Institution of Washington. It was one of the first attempts to create a predictive equation for BMR and remained the standard for decades.
The version we use is the 1984 revision by Roza and Shizgal, which updated the original coefficients based on more modern data and measurement techniques.
The Equations
BMR = 88.362 + (13.397 × weightkg) + (4.799 × heightcm) − (5.677 × ageyears)BMR = 447.593 + (9.247 × weightkg) + (3.098 × heightcm) − (4.330 × ageyears)When to Consider This Formula
- Historical comparison with older research
- If Mifflin-St Jeor results seem inconsistent with your experience
- Cross-validation of results using multiple methods
3. Katch-McArdle Equation
Background
Unlike other equations that use total body weight, the Katch-McArdle formula uses lean body mass (LBM) — your weight minus fat mass. This approach is based on the principle that metabolically active tissue (muscle, organs) drives BMR, not fat tissue.
This makes it potentially more accurate for individuals who know their body fat percentage, particularly athletes or those with unusual body compositions (very muscular or very lean).
The Equation
BMR = 370 + (21.6 × LBMkg)Example Calculation
80kg person with 20% body fat:
LBM = 80 × (1 − 0.20) = 80 × 0.80 = 64 kg
BMR = 370 + (21.6 × 64) = 370 + 1382.4 = 1,752 calories/day
When to Use This Formula
- You know your body fat percentage (from DEXA, calipers, or reliable estimation)
- You're an athlete or have higher-than-average muscle mass
- You're very lean (under 15% for men, under 22% for women)
- Other formulas seem significantly inaccurate for you
📊 Formula Comparison Summary
| Formula | Year | Inputs Required | Best For | Accuracy* |
|---|---|---|---|---|
| Mifflin-St Jeor | 1990 | Weight, Height, Age, Sex | General population | ±10% for ~82% |
| Harris-Benedict | 1984 (revised) | Weight, Height, Age, Sex | Historical comparison | ±10% for ~75% |
| Katch-McArdle | Various | Lean Body Mass | Athletes, known BF% | Depends on BF% accuracy |
*Accuracy refers to the percentage of people for whom the formula predicts measured metabolic rate within 10%. Based on Frankenfield et al., 2005.
Activity Level Multipliers
After calculating BMR, we multiply by an activity factor to account for daily movement, exercise, and the thermic effect of food. These multipliers are derived from research on physical activity levels (PAL) conducted by the Food and Agriculture Organization (FAO), World Health Organization (WHO), and United Nations University (UNU).
| Activity Level | Multiplier | Description | Examples |
|---|---|---|---|
| Sedentary | 1.2 | Little or no exercise, desk job | Office worker who drives to work, minimal walking, no structured exercise |
| Lightly Active | 1.375 | Light exercise 1-3 days/week | Desk job but walks 30 min most days, or 1-2 gym sessions/week |
| Moderately Active | 1.55 | Moderate exercise 3-5 days/week | Regular gym-goer (3-5x/week), active hobbies, 7,500+ steps daily |
| Very Active | 1.725 | Hard exercise 6-7 days/week | Intense training 6-7 days, active job, or training for competition |
| Extremely Active | 1.9 | Very hard exercise + physical job | Professional athlete, construction worker who also trains, 2+ workouts/day |
💡 Tips for Choosing Your Activity Level
- Be honest and conservative: Most people overestimate their activity level. If unsure, choose one level lower than you think.
- Consider your whole day: A 1-hour workout in an otherwise sedentary day doesn't make you "Very Active."
- Think weekly average: If you exercise 3 days but are sedentary 4 days, you're closer to "Lightly Active."
- Job matters: A nurse on their feet all day has higher baseline activity than an office worker, even without formal exercise.
- NEAT is significant: Non-Exercise Activity Thermogenesis (fidgeting, walking, standing) can vary by 500+ calories between individuals.
Macronutrient Calculations
Our calculator provides suggested macronutrient (protein, carbohydrates, fat) distributions based on your calculated TDEE. These are general guidelines based on established nutritional science, not personalized recommendations.
Caloric Values of Macronutrients
Our Preset Distributions
Balanced (Default)
General health, sustainable eating, most activity types
Low Carb
Reduced carbohydrate intake, higher fat for satiety
High Protein
Muscle building, weight loss while preserving muscle
Example Calculation
For 2,000 calorie TDEE with Balanced distribution:
- Protein (30%): 2000 × 0.30 = 600 cal ÷ 4 = 150g protein
- Carbs (40%): 2000 × 0.40 = 800 cal ÷ 4 = 200g carbs
- Fat (30%): 2000 × 0.30 = 600 cal ÷ 9 = 67g fat
Accuracy & Validation Research
Understanding the accuracy of BMR/TDEE equations helps set appropriate expectations. Here's what peer-reviewed research tells us:
Key Validation Studies
Frankenfield et al. (2005) — Comprehensive Comparison
This systematic review, published in the Journal of the American Dietetic Association, compared multiple predictive equations against indirect calorimetry (the gold standard for measuring metabolic rate) across 173 studies.
Key Findings:
- Mifflin-St Jeor was the most accurate for non-obese individuals (82% within 10%)
- Mifflin-St Jeor was also most accurate for obese individuals (70% within 10%)
- Harris-Benedict tended to overestimate BMR, especially in obese individuals
- No equation was accurate for more than 82% of subjects
Conclusion: The Mifflin-St Jeor equation is the most reliable for estimating resting metabolic rate in both non-obese and obese individuals.
Amaro-Gahete et al. (2019) — Young Adults
This study evaluated BMR prediction equations in 85 young adults (18-25 years) using indirect calorimetry.
Key Findings:
- Mifflin-St Jeor showed the smallest bias in young adults
- Harris-Benedict slightly overestimated BMR
- Individual variation remains significant regardless of equation used
What "Accuracy" Actually Means
When we say an equation is "accurate within 10% for 82% of people," this means:
- For 82 out of 100 people, the predicted value will be within ±10% of their actual measured BMR
- For 18 out of 100 people, the error will be greater than 10%
- On a 1,500 calorie BMR, ±10% means the true value could be 1,350-1,650 calories
This is why we emphasize using calculated TDEE as a starting point and adjusting based on real-world results.
Known Limitations
We believe transparency about limitations is as important as explaining the methodology. Here are the key factors that can cause calculator estimates to differ from your actual needs:
Genetic Variation
Metabolic rate has a genetic component. Studies on identical twins show that genetics can account for 40-70% of the variation in BMR between individuals of similar size, age, and sex.
Body Composition
Muscle tissue burns more calories than fat tissue at rest. Two people of identical weight but different muscle/fat ratios can have significantly different BMRs. Only Katch-McArdle accounts for this, and it requires accurate body fat measurement.
Hormones & Medications
Thyroid hormones, cortisol, insulin, and other factors significantly affect metabolic rate. Medications (beta-blockers, antidepressants, steroids, etc.) can also alter metabolism in ways not captured by predictive equations.
Metabolic Adaptation
During prolonged caloric restriction, your body can reduce metabolic rate beyond what weight loss alone would predict (adaptive thermogenesis). This is not reflected in calculator estimates.
Population Specificity
Most BMR equations were developed on predominantly Western populations. Accuracy may vary for individuals of different ethnic backgrounds due to differences in body composition and metabolic characteristics.
Activity Level Estimation
Activity multipliers are broad categories. NEAT (Non-Exercise Activity Thermogenesis) can vary by 500+ calories between "fidgety" and "still" individuals, and is impossible to quantify with a questionnaire.
Environmental Factors
Temperature extremes, altitude, illness, stress, and sleep quality all affect metabolic rate and are not accounted for in standard equations.
Age-Related Changes
While equations include age, they use linear relationships. Actual metabolic changes with age are more complex, especially during puberty, menopause, and advanced age.
How to Use These Estimates Effectively
Given the limitations above, here's our recommended approach for using TDEE calculations as part of your nutrition strategy:
Calculate Your Starting Point
Use our calculator with the Mifflin-St Jeor equation (recommended for most people). Be honest about your activity level—when in doubt, choose one level lower.
Track Consistently for 2-4 Weeks
Eat at or near your calculated TDEE (or target, if trying to lose/gain weight) and track your food intake as accurately as possible. Weigh yourself daily at the same time (morning, after bathroom) and record it.
Analyze Weekly Averages
Daily weight fluctuates due to water, food volume, and other factors. Look at weekly averages instead. After 2-4 weeks, you should see a trend.
- Weight stable? Your estimated TDEE is approximately correct.
- Losing weight unexpectedly? Your true TDEE may be higher.
- Gaining weight unexpectedly? Your true TDEE may be lower.
Adjust in Small Increments
If results don't match expectations, adjust your intake by 100-200 calories and observe for another 2 weeks. Small adjustments are easier to sustain and give clearer feedback than large changes.
Recalculate Periodically
As your weight, age, or activity level changes, your TDEE changes too. Recalculate every 5-10 kg of weight change, when your activity patterns change significantly, or every 4-6 weeks during active weight loss.
Seek Professional Guidance When Needed
For specific health conditions, medical nutrition therapy, eating disorder recovery, or when results don't make sense despite accurate tracking, consult a registered dietitian or healthcare provider. A calculator can't replace professional assessment.
Scientific References
All formulas and claims on this page are based on peer-reviewed scientific literature. Below are the primary sources:
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1Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. "A new predictive equation for resting energy expenditure in healthy individuals." American Journal of Clinical Nutrition. 1990;51(2):241-247. PubMed: 2305711
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2Roza AM, Shizgal HM. "The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass." American Journal of Clinical Nutrition. 1984;40(1):168-182. PubMed: 6741850
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3McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. 8th Edition. Lippincott Williams & Wilkins; 2014.
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4Frankenfield D, Roth-Yousey L, Compher C. "Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review." Journal of the American Dietetic Association. 2005;105(5):775-789. PubMed: 15883556
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5FAO/WHO/UNU Expert Consultation. "Human energy requirements: Report of a Joint FAO/WHO/UNU Expert Consultation." Food and Agriculture Organization of the United Nations. Rome, 2004. FAO Report
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6U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. DietaryGuidelines.gov
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7Amaro-Gahete FJ, et al. "Validity of predictive equations for basal metabolic rate in Spanish young adults." Nutrients. 2019;11(11):2635. PubMed: 31684190
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8Müller MJ, Bosy-Westphal A, Kutzner D, Heller M. "Metabolically active components of fat-free mass and resting energy expenditure in humans." American Journal of Physiology-Endocrinology and Metabolism. 2002;283(2):E289-E297. PubMed: 12110533
Disclaimer
The information on this page is provided for educational and informational purposes only. It is not intended as medical advice, diagnosis, or treatment, nor as a substitute for professional nutritional counseling.
The formulas and methods described are mathematical estimates based on population averages. Your individual metabolic rate may differ significantly from calculated values due to factors including but not limited to: genetics, hormonal status, medication use, body composition, and health conditions.
Always consult with a qualified healthcare provider or registered dietitian before making significant changes to your diet or exercise routine, especially if you have any medical conditions, are pregnant or nursing, have a history of eating disorders, or are taking medications.
Last reviewed and updated: June 1, 2026
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