About & Methodology

How our calculators work, the formulas they use, and where the numbers come from.

What this site does

This site provides five free calculators for everyday health and fitness planning: TDEE (Total Daily Energy Expenditure), BMR (Basal Metabolic Rate), Macros (protein/carbs/fat), Protein targets, and BMI (Body Mass Index). All calculators run entirely in your browser — no data is sent to a server, no account is required, and no information is stored.

Every formula used is published, peer-reviewed, and widely cited in nutrition and exercise science research. We link to primary sources below so you can verify the methodology yourself.

Formulas used

Mifflin–St Jeor (1990) — primary BMR formula

Used as the default formula across all calculators. Validated against doubly-labeled water studies (the gold standard for measuring energy expenditure) and found to be the most accurate predictive equation for the general population, predicting BMR within 10% for approximately 82% of subjects.

Male: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Female: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Katch–McArdle (1996) — used when body fat % is provided

Based on lean body mass (LBM) rather than total weight. More accurate for individuals with body composition that differs significantly from population averages — athletes, bodybuilders, or people with higher body fat percentages.

LBM = weight in kg × (1 − body fat % / 100)
BMR = 370 + (21.6 × LBM)

Harris–Benedict (1919, revised 1984)

The original BMR equation, still widely referenced in clinical settings. The 1984 revision by Roza and Shizgal improved on the original. Tends to slightly overestimate BMR compared to Mifflin–St Jeor for most modern populations.

Male: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age)
Female: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)

TDEE — activity multipliers

TDEE is calculated as BMR × an activity factor. These multipliers are based on the commonly used Harris–Benedict activity scale, refined through subsequent research:

Sedentary (little/no exercise): ×1.2
Lightly active (1–2 days/week): ×1.375
Moderately active (3–5 days/week): ×1.55
Very active (6–7 days/week): ×1.725
Athlete (2x/day training): ×1.9

BMI — Quetelet Index

Developed by Adolphe Quetelet in the 1830s. Still the WHO standard for population-level weight screening.

BMI = weight in kg / (height in m)²

Ideal weight — Devine formula (1974)

Originally developed for drug dosage calculations, now commonly used as a quick reference for "ideal" weight. Provided as one reference point among several reasonable approaches — the WHO healthy BMI range (18.5–24.9) is generally a more useful target range than a single number.

Male: IBW (kg) = 50 + 2.3 × (height in inches − 60)
Female: IBW (kg) = 45.5 + 2.3 × (height in inches − 60)

Macro & protein targets

Protein recommendations (1.6–2.4 g/kg depending on goal and activity level) are based on position stands from the International Society of Sports Nutrition and systematic reviews of protein intake studies in resistance-trained populations. Macro splits (protein/carb/fat percentages) for cutting, maintaining, and bulking reflect commonly recommended ranges from sports nutrition literature, prioritising protein for lean mass preservation during deficits and adequate fat intake for hormonal health.

Sources & further reading

Key research referenced

Mifflin MD, St Jeor ST, et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition.
Katch FI, McArdle WD (1996). Introduction to Nutrition, Exercise, and Health.
Harris JA, Benedict FG (1919). A Biometric Study of Basal Metabolism in Man.
Roza AM, Shizgal HM (1984). The Harris Benedict equation reevaluated. American Journal of Clinical Nutrition.
World Health Organization. Body Mass Index classification.
International Society of Sports Nutrition. Position Stand: protein and exercise.
Devine BJ (1974). Gentamicin therapy. Drug Intelligence and Clinical Pharmacy.

Disclaimer

This tool provides estimates for general informational purposes only and is not medical advice. Results are based on population-average formulas and may not accurately reflect individual variation due to genetics, medical conditions, medications, or other factors. Always consult a qualified healthcare provider, registered dietitian, or physician before making significant changes to your diet or exercise routine — particularly if you have any existing health conditions, are pregnant or breastfeeding, or are under 18.