Sources & methods
Every calculator on VitalMetrics uses a published equation or guideline. Here they all are in one place, so you, or your clinician, can check exactly what the numbers mean.
| Calculator | Formula / threshold | Reference |
|---|---|---|
| BMI, BMI chart | kg ÷ m²; categories 18.5 / 25 / 30 / 35 / 40 | World Health Organization; CDC adult BMI categories; WHO Expert Consultation, Lancet 2004;363:157–163 |
| BMR, TDEE, calories, macros | Mifflin-St Jeor: 10W + 6.25H − 5A + 5 / −161 | Mifflin MD et al., Am J Clin Nutr 1990;51:241–247; Frankenfield D et al., J Am Diet Assoc 2005;105:775–789 |
| BMR, TDEE | Revised Harris-Benedict (Roza & Shizgal) | Roza AM, Shizgal HM, Am J Clin Nutr 1984;40:168–182 |
| BMR, TDEE | Katch-McArdle: 370 + 21.6 × LBM | McArdle WD, Katch FI, Katch VL, Exercise Physiology |
| Calorie goals | ≈ 7,700 kcal per kg; floors 1,200 / 1,500 kcal | NIDDK Body Weight Planner (Hall KD et al., Lancet 2011); Harvard Health Publishing |
| Macros | AMDR carbs 45–65%, fat 20–35%, protein 10–35%; 4/4/9 kcal per g | Institute of Medicine, Dietary Reference Intakes for Macronutrients (2005) |
| Protein | RDA 0.8 g/kg; active 1.2–2.0 g/kg; 65+ 1.0–1.2 g/kg | IOM 2005; Jäger R et al., JISSN 2017;14:20; Morton RW et al., BJSM 2018;52:376; Bauer J et al., JAMDA 2013;14:542 |
| Body fat | US Navy circumference equations | Hodgdon JA, Beckett MB, Naval Health Research Center reports 84-11 & 84-29 (1984); ACE body fat categories |
| Body fat (comparison) | Deurenberg: 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4 | Deurenberg P et al., Br J Nutr 1991;65:105–114 |
| Lean body mass | Boer equations | Boer P, Am J Physiol 1984;247:F632–F636 |
| Ideal weight | Devine, Robinson, Miller, Hamwi | Devine 1974; Robinson 1983; Miller 1983; Hamwi 1964 |
| Waist-to-height | Bands 0.4 / 0.5 / 0.6 | NICE CG189 update (2022); Ashwell M et al., Obes Rev 2012;13:275–286 |
| Waist-to-hip | Cut-offs 0.90 men, 0.85 women | WHO Expert Consultation on waist circumference and waist–hip ratio (2008) |
| Due date, pregnancy week | LMP + 280 d (cycle-adjusted); conception + 266 d; IVF day-5 + 261 d, day-3 + 263 d | ACOG Committee Opinion 700 (2017); ACOG Committee Opinion 579 (term definitions) |
| Ovulation, conception | Ovulation ≈ next period − 14 d; six-day fertile window | Wilcox AJ et al., N Engl J Med 1995;333:1517–1521; MedlinePlus |
| Heart rate zones | Tanaka 208 − 0.7A; Fox 220 − A; Gulati 206 − 0.88A; Karvonen | Tanaka H et al., JACC 2001;37:153; Gulati M et al., Circulation 2010;122:130; Karvonen MJ 1957; AHA target heart rates |
| Calories burned | MET × kg × hours | 2024 Adult Compendium of Physical Activities (Herrmann SD et al., J Sport Health Sci 2024;13:6–12) |
| One-rep max | Epley; Brzycki | Epley B 1985; Brzycki M, JOPERD 1993;64:88–90; NSCA Essentials |
| Water intake | AI 3.7 L men, 2.7 L women (≈80% from drinks) | National Academies, DRI for Water and Electrolytes (2005) |
| Body surface area | Mosteller √(cm × kg / 3600) | Mosteller RD, N Engl J Med 1987;317:1098 |
How we handle limits
Most of these formulas were derived from specific groups of healthy adults. They can be off for children, pregnant people (except the pregnancy tools), older adults, very muscular or very lean people, and people with medical conditions. We say so on each page and flag results outside a formula’s usable range.
We round only for display; calculations keep full precision. Dates are calculated on your device in your local time zone.
Spotted an error? Accuracy matters on a health site. The formulas live in one file of the open code (app/utils/health.ts) so they are easy to audit.