Methodology

Overview

This calculator estimates resting energy needs, multiplies that estimate by an activity factor, and then applies the selected calorie goal. The output is an informational starting point for personal tracking, not an exact measurement or individualized recommendation.

All calculator inputs are processed locally in your browser. The app does not require an account and does not store calculator inputs on a server.

Formula Inputs and Gender Coefficients

The Mifflin-St Jeor and Revised Harris-Benedict equations use male/female coefficients from their published formulas. The form labels this field as Gender for readability, but internally the selected option is used only to choose the equation coefficient. The calculator cannot model all individual biological variation.

Mifflin-St Jeor Equation

This is the default equation for most adult users because it is widely cited and performed well in comparisons against measured resting metabolic rate.

Revised Harris-Benedict Equation

This option uses the 1984 Roza and Shizgal revision of the original Harris-Benedict equation.

Katch-McArdle Equation

Katch-McArdle estimates resting needs from lean body mass. It is only available when body fat percentage is entered. If body fat is guessed poorly, this equation can be less useful than the default.

Unit Conversion Logic

Activity Multipliers

Estimated TDEE is calculated as BMR multiplied by the selected activity factor.

These are broad categories. If you are unsure, start conservative and adjust after observing real-world progress.

Goal Calories

Goal calories are a percentage adjustment from estimated TDEE:

Macro Calculation

Macros use goal-adjusted calories and body weight. Protein is set first, fat is set as a percentage of calories, and carbohydrates receive the remaining calories.

• Balanced: protein 1.8 g/kg, fat 27.5% of calories.
• Higher Protein: protein 2.2 g/kg, fat 25% of calories.
• Lower Fat: protein 1.8 g/kg, fat 20% of calories.
• Lower Carb: protein 2.0 g/kg, fat 40% of calories.

These presets are educational estimates. They do not replace individualized nutrition advice.

Rounding and Estimate Range

• Displayed calories are rounded to the nearest 5 kcal.
• The practical TDEE range is shown as +/-10% of estimated TDEE.
• The weekly direction in the result panel uses the simplified 3,500 kcal per pound heuristic and is shown only as context.

Conservative Warnings

The calculator warns when goal calories fall below 1,500 kcal/day for male coefficients or 1,200 kcal/day for female coefficients. This warning is intentionally conservative and does not determine whether a target is appropriate for you — it is a flag for your own tracking review.

This tool is designed for adults using it as a nutrition logging and awareness utility. Users under 18 should use it only with appropriate oversight. It is not a substitute for individualized nutrition planning.

Limitations

• Predictive equations estimate population averages, not exact individual needs.
• Activity multipliers are coarse and self-reported activity is often inaccurate.
• Food labels, portion estimates, and tracking consistency add measurement error.
• Energy expenditure can change with weight loss, training load, sleep, stress, and routine shifts.

Use the result as a starting point. Track weight averages and energy for 2-4 weeks, then adjust gradually if needed.

References

1. National Academies of Sciences, Engineering, and Medicine — Factors Affecting Energy Expenditure and Requirements. Dietary Reference Intakes for Energy — NCBI Bookshelf, 2023.Defines TDEE components (REE, TEF, PAEE) and explains why population equations cannot capture individual metabolic variation.
2. 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, 1990.Primary source for the Mifflin-St Jeor BMR equation used as the default in this calculator.
3. 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, 1984.Source for the revised Harris-Benedict coefficients — default equation on this calculator page.
4. McArdle WD, Katch FI, Katch VL — Exercise Physiology: Energy, Nutrition, and Human Performance. Lippincott Williams & Wilkins, 7th edition, 2010.Textbook reference for the lean-body-mass-based Katch-McArdle resting energy estimate.
5. Frankenfield D, Roth-Yousey L, Compher C — Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults. J Am Diet Assoc. 2005;105(5):775-789, 2005.Meta-analysis showing Mifflin-St Jeor within ~10% of measured RMR for ~82% of non-obese and ~70% of obese adults — supports honest accuracy framing.
6. Chao AM, Tronieri JS, Alamuddin N, Wadden TA — Behavioral Approaches to Obesity Management. Endotext — NCBI Bookshelf, 2026.Supports evidence-aware wording around structured calorie deficits and behavioral weight management.
7. Institute of Medicine, Food and Nutrition Board — Acceptable Macronutrient Distribution Ranges. Dietary Reference Intakes — summary table (NCBI Bookshelf), 2003.Provides AMDR context (10–35% protein, 20–35% fat, 45–65% carbs) for balanced macro presets.
8. Jager R, Kerksick CM, Campbell BI, et al. — International Society of Sports Nutrition Position Stand: Protein and Exercise. J Int Soc Sports Nutr. 2017;14:20, 2017.Supports 1.6–2.2 g/kg/day protein ranges for many exercising adults — basis for protein and macro guidance.
9. Hall KD, Sacks G, Chandramohan D, et al. — Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837, 2011.Shows weight change is slow and non-linear over time — supports labeling the 3,500 kcal/lb rule as a rough heuristic, not a law.
10. Dhurandhar NV, Schoeller D, Brown AW, et al. — Energy balance measurement: when something is not better than nothing. Int J Obes (Lond). 2015;39(7):1109-1113, 2015.Documents systematic overreporting of exercise and underreporting of food — supports activity-level conservatism guidance.
11. Bassett DR Jr, Toth MJ, Poehlman ET — Energy Expenditure Determined by Self-Reported Physical Activity Is Related to Body Fatness. Obes Res. 1999;7(6):567-573, 1999.Shows self-reported activity duration and intensity are unreliable — especially at higher body fat percentages.
12. Morton RW, Murphy KT, McKellar SR, et al. — A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376-384, 2018.Meta-analysis finding ~1.6 g/kg/day as an inflection point for muscle gain — supports protein calculator ranges.
13. Helms ER, Aragon AA, Fitschen PJ — Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20, 2014.Supports higher protein intakes during caloric deficits to preserve lean mass.
14. Frankenfield DC, Rowe WA, Smith JS, Cooney RN — Validation of several established equations for resting metabolic rate in obese and nonobese people. J Am Diet Assoc. 2003;103(9):1152-1159, 2003.Direct validation showing standard Harris-Benedict within ±10% of measured RMR in ~67% of adults vs ~78% for Mifflin-St Jeor in the same cohort.
15. Harris JA, Benedict FG — A Biometric Study of Basal Metabolism in Man. Carnegie Institution of Washington Publication No. 279, 1919.Original Harris-Benedict basal metabolism equations (1919) — historical baseline superseded by the 1984 revision for most modern adults.
16. O'Neill JER, Corish CA, Horner K — Accuracy of Resting Metabolic Rate Prediction Equations in Athletes: A Systematic Review with Meta-analysis. Sports Med. 2023;53(12):2373-2398, 2023.Athlete systematic review and meta-analysis — several common equations including Mifflin-St Jeor and Owen differed significantly from measured RMR in pooled athlete data; lean-mass equations (e.g., Cunningham 1980) and Ten-Haaf performed differently by population, with no single best equation for all athletes.
17. Cunningham JJ — A reanalysis of the factors influencing basal metabolic rate in normal adults. Am J Clin Nutr. 1980;33(11):2372-2374, 1980.Primary source for the Cunningham equation (500 + 22 × lean body mass kg). Cunningham’s paper labels the output BMR; the 1980 reanalysis of Harris-Benedict (1919) data found LBM as the single predictor, with sex and age adding little once LBM was included.
18. Schofield WN — Predicting basal metabolic rate, new standards and review of previous work. Hum Nutr Clin Nutr. 1985;39 Suppl 1:5-41, 1985.Primary source for the Schofield age- and sex-specific BMR predictive equations (weight-only kcal/day form retained in FAO/WHO Table 5.2).
19. FAO/WHO/UNU — Human Energy Requirements — Report of a Joint FAO/WHO/UNU Expert Consultation. FAO Food and Nutrition Technical Report Series, 2001.Table 5.2 Schofield (1985) kcal/day coefficients by age and sex; documents retention of these equations and notes on geographic/ethnic applicability limits.
20. Owen OE, Kavle EC, Owen RS, Polansky M, Caprio S, Mozzoli MA, Kendrick ZV, Bushman MC, Boden G — A reappraisal of caloric requirements in healthy women. Am J Clin Nutr. 1986;44(1):1-19, 1986.Primary source for Owen female RMR equations — non-athlete (795 + 7.18 × weight kg) and athlete (50.4 + 21.1 × weight kg) variants.
21. Owen OE, Holup JL, D'Alessio DA, Craig ES, Polansky M, Smalley KJ, Kavle EC, Bushman MC, Owen LR, Mozzoli MA, Kendrick ZV, Boden G — A reappraisal of the caloric requirements of men. Am J Clin Nutr. 1987;46(6):875-885, 1987.Primary source for Owen male RMR equation (879 + 10.2 × weight kg) in men 18–82 years; found weight alone predicted RMR with age effect trivial.
22. de Boer P — Estimated lean body mass as an index for normalization of body fluid volumes in humans. Am J Physiol. 1984;247(4 Pt 2):F632-F636, 1984.Primary source for the Boer (1984) sex-specific anthropometric lean body mass equations — widely used in pharmacology and clinical normalization.
23. James WPT — Research on obesity: a report of the DHSS/MRC group. HM Stationery Office, London. ISBN 0114500347, 1976.DHSS/MRC report containing the sex-specific quadratic LBM equations commonly cited as James (1976) in nutrition and clinical tools; some pharmacology sources attribute the quadratic form to work cited within the report (e.g., Eddy).
24. Hume R — Prediction of lean body mass from height and weight. J Clin Pathol. 1966;19(4):389-392, 1966.Classic linear sex-specific anthropometric lean body mass prediction — older than Boer/James; useful for comparison but often diverges from modern DEXA cohorts.
25. Hodgdon JA, Beckett MB — Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center Technical Report 84-11, 1984; companion report 84-29 for women, 1984.IOM/NAP summary documents the Hodgdon & Beckett (1984) U.S. Navy circumference body-fat equations (NHRC reports 84-11 and 84-29) used when Navy body fat % is selected in this calculator.

Questions or Corrections

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