Methodology

Every equation, and where it came from.

If a calculator won't tell you what it is doing, you have no way to judge whether its answer is any good. This page lists every formula in our engine.

How the calculators are built

All maths lives in a single open-source module with unit tests covering every formula. The interface is separate from the calculation, so what you see on screen is exactly what the tested code produces. You can read both on GitHub.

Calculations run entirely in your browser. Nothing you enter is transmitted, logged, or stored.

Formulas in use

Basal metabolic rate

Default when body fat is unknown

Mifflin-St Jeor

Mifflin MD, St Jeor ST, et al. Am J Clin Nutr, 1990

Comparison / legacy

Revised Harris-Benedict

Roza AM, Shizgal HM, 1984

Default when body fat is supplied

Katch-McArdle

Katch & McArdle

Athletic populations; runs higher

Cunningham

Cunningham JJ, 1980

Weight-only simple estimate

Owen

Owen OE, et al. 1986–87

Body composition

Tape-measure body fat, ±3.5%

U.S. Navy circumference

Hodgdon JA, Beckett MB, 1984

BMI-based body fat, ±5%

Deurenberg

Deurenberg P, et al. 1991

Lean mass normalised for height

FFMI

Kouri EM, et al. 1995

Cardiometabolic risk; outperforms BMI

Waist-to-height ratio

Ashwell M, Gibson S, 2016

Macronutrients

≈2.2 g/kg LBM when body fat known, else ≈1.8 g/kg bodyweight

Protein from lean mass

Helms ER, et al. Int J Sport Nutr Exerc Metab, 2014; Morton RW, et al. Br J Sports Med, 2018

Minimum 0.8 g/kg bodyweight for hormonal health

Fat floor

Helms ER, et al. The Muscle and Strength Pyramid

Fills the remaining calorie budget

Carbohydrate

Derived

What these numbers are not

Every equation here was fitted to a population, not to you. Two people matching on age, sex, height and weight can differ by several hundred calories a day in real expenditure, largely through unconscious activity.

Treat any output as a starting estimate. Run it for two to three weeks, track a weekly average bodyweight, and adjust from what actually happened. That feedback loop beats any formula.

These tools do not diagnose, treat, or replace clinical advice. If you have a medical condition, are pregnant, or are managing an eating disorder, talk to a clinician who knows your history.

Corrections

If a formula is misapplied or a citation is wrong, we want to know. Open an issue on GitHub with the inputs and the result you expected. Corrections are logged in public and articles carry a visible last-updated date.