How Our Calculators Work

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HealthCalc uses peer-reviewed medical equations for every calculator. Each formula is cited with its original study, and all calculations run entirely in your browser — we never transmit or store your health data.

Formula Sources

BMI — Body Mass Index

BMI = weight (kg) ÷ height² (m²)

Also known as the Quetelet Index, developed by Adolphe Quetelet in the 1830s.

Source: World Health Organization. "Body mass index — BMI." WHO, 2000. WHO Reference

BMR — Basal Metabolic Rate

Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(y) + 5

Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(y) − 161

Source: 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. DOI: 10.1093/ajcn/51.2.241

TDEE — Total Daily Energy Expenditure

TDEE = BMR × activity multiplier (1.2 sedentary → 1.9 very active)

Based on the Harris-Benedict activity factors applied to the Mifflin-St Jeor BMR estimate.

Source: Harris JA, Benedict FG. "A biometric study of human basal metabolism." Proc Natl Acad Sci USA. 1918;4(12):370–373. DOI: 10.1073/pnas.4.12.370

Water Intake

~3.7 L/day (men) • ~2.7 L/day (women) — adjusted by activity level

Total water intake from all beverages and food. Our calculator adjusts the baseline recommendation for individual activity levels and climate.

Source: National Academies of Sciences, Engineering, and Medicine. "Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate." Washington, DC: The National Academies Press; 2004. DOI: 10.17226/10996

Body Fat Percentage — US Navy Method

Estimates body fat using neck, waist, and hip circumference (for women) or neck and waist circumference (for men) with height as a reference.

Source: Hodgdon JA, Beckett MB. "Prediction of percent body fat for U.S. Navy men and women from body circumferences and height." Naval Health Research Center Report. 1984. Report No. 84-08.

Ideal Body Weight

Our calculator computes four well-known estimates:

Hamwi (1964): Men: 48 kg + 2.7 kg per inch over 5 ft • Women: 45.5 kg + 2.2 kg per inch over 5 ft

Devine (1974): Men: 50 + 2.3 × (inches over 60) • Women: 45.5 + 2.3 × (inches over 60)

Robinson (1983): Men: 52 + 1.9 × (inches over 60) • Women: 49 + 1.7 × (inches over 60)

Miller (1983): Men: 56.2 + 1.41 × (inches over 60) • Women: 53.1 + 1.36 × (inches over 60)

Sources: Hamwi GJ. "Changing dietary patterns." Am J Clin Nutr. 1964;15:323–324. • Devine BJ. "Gentamicin therapy." Drug Intell Clin Pharm. 1974;8:650–655. • Robinson JD, Lupkiewicz SM, Palenik L, et al. "Determination of ideal body weight for drug dosage calculations." Am J Hosp Pharm. 1983;40:1016–1019. • Miller DW Jr, Bachynsky FE. "A comparison of two methods for estimating ideal body weight." Clin Pharm. 1983;2:464–468.

Macronutrient Calculator

Distributes daily calories across protein, carbohydrates, and fat based on the Acceptable Macronutrient Distribution Ranges (AMDR) set by the Institute of Medicine. The default split is 45% carbs, 25% protein, 30% fat.

Source: Institute of Medicine. "Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids." Washington, DC: The National Academies Press; 2005. DOI: 10.17226/10490

Calorie Deficit Calculator

1 lb of body fat ≈ 3,500 kcal deficit

Calculates the daily caloric deficit needed to reach a target weight loss over a given time frame. This 3,500 kcal per pound approximation is widely used as a clinical guideline.

Source: Hall KD, Sacks G, Chandramohan D, et al. "Quantification of the energy balance for weight management." Int J Obes. 2011;35:1–6. DOI: 10.1038/ijo.2011.105

Keto Macro Calculator

Standard ketogenic ratio: 70% fat • 25% protein • 5% net carbs (≤ 50 g/day)

Calculates macronutrient targets for a standard ketogenic diet based on total daily calorie needs. Net carbs are calculated as total carbs minus fiber.

Source: Paoli A, Rubini A, Volek JS, Grimaldi KA. "Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets." Eur J Clin Nutr. 2013;67(8):789–796. DOI: 10.1038/ejcn.2013.116

Heart Rate Zone Calculator

Target HR = ((max HR − resting HR) × %intensity) + resting HR

Max HR = 220 − age

Uses the Karvonen formula to calculate heart rate zones based on heart rate reserve (HRR), which accounts for your resting heart rate for more personalized zones than simple percentage of max HR alone.

Source: Karvonen MJ, Kentala K, Mustala O. "The effects of training on heart rate: a longitudinal study." Ann Med Exp Biol Fenn. 1957;35(3):307–315.

Body Surface Area

Mosteller: BSA = √[(height(cm) × weight(kg)) / 3600]

DuBois: BSA = 0.007184 × height(cm)^0.725 × weight(kg)^0.425

Two formulas are provided. The Mosteller formula is the most commonly used in clinical settings for its simplicity. The DuBois formula is a historical reference standard.

Source: Mosteller RD. "Simplified calculation of body-surface area." N Engl J Med. 1987;317(17):1098. DOI: 10.1056/NEJM198710223171717

VO2 Max Estimate

Cooper run: VO2 max = (483 / time(min)) + 3.5

Resting HR: VO2 max = 15.3 × (max HR / resting HR)

Two estimation methods: the Cooper 1.5-mile run/walk test (requires you to time yourself), and a resting heart rate method that does not require exercise.

Source: Cooper KH. "A means of assessing maximal oxygen intake: field tests of cardiorespiratory fitness." JAMA. 1968;203(3):201–204. DOI: 10.1001/jama.1968.03140030033008

Lean Body Mass

Men: LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2

Women: LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3

The Boer formula estimates lean body mass (all non-fat tissue — muscle, bone, water, organs) using only weight and height. It is commonly used in pharmacokinetic dosing.

Source: Boer P. "Estimated lean body mass as an index for normalization of body fluid volumes in man." Am J Physiol. 1984;246(5):F632—F636. DOI: 10.1152/ajprenal.1984.246.5.F632

Disclaimer

All calculators are for informational and educational purposes only. They are not intended to diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare provider for medical advice.