How We Calculate

Mifflin-St Jeor Equation (primary)

Our primary formula for estimating Basal Metabolic Rate (BMR) — the calories burned at complete rest. Developed from data on 498 healthy subjects aged 19–78 using indirect calorimetry.

Accuracy: A 2005 systematic review found this equation predicted RMR within 10% of measured values for more individuals than any other tested formula — 82% of non-obese and 70% of obese subjects.

Limitation: Like all population-based formulas, it doesn’t account for individual variation in muscle mass, hormones, or metabolic adaptation. Actual metabolic rate may differ by ±10–15%.

Harris-Benedict Equation (revised, secondary)

The original Harris-Benedict equation dates to 1919. We use the revised 1984 version by Roza and Shizgal, which corrected systematic overestimation. Shown alongside Mifflin-St Jeor for comparison.

Activity multipliers (TDEE): We multiply BMR by the standard Katch-McArdle activity factors: Sedentary ×1.2 · Lightly active ×1.375 · Moderately active ×1.55 · Very active ×1.725 · Extremely active ×1.9.

US Navy Circumference Method (Hodgdon & Beckett, 1984)

Developed at the Naval Health Research Center in San Diego, this method estimates body fat percentage from simple tape measurements. It was validated against hydrostatic (underwater) weighing data from large samples of military personnel, and has since become the official body composition screening protocol for all US Department of Defense branches.

Accuracy: Approximately ±3–4% compared to DEXA scanning. More reliable than bioelectrical impedance (BIA) scales, which are heavily affected by hydration. Best used for tracking trends over time rather than as an absolute measure.

Four published ideal body weight formulas

We show four formulas side by side, all originally developed for clinical pharmacology (drug dosing based on lean body mass) rather than aesthetic goals. Heights below 5 ft (152 cm) use base weights only with no inch adjustment.

We also show the healthy BMI range (18.5–24.9 kg/m²) from the World Health Organization as a practical reference alongside the formula results.

Epley, Brzycki & Lombardi formulas

We calculate and display three 1RM estimates simultaneously, with the Epley formula used as the primary figure for the percentage training chart. All three originate from strength and conditioning practice rather than large randomised trials — they are widely used empirical tools validated through decades of application.

Accuracy note: All formulas are most accurate when used with sets of 3–8 reps. Estimates become progressively less reliable beyond 10 reps, as endurance and technique factors increasingly influence performance at lighter loads.

MET values — Compendium of Physical Activities

MET (Metabolic Equivalent of Task) values for all 40+ activities come from the Compendium of Physical Activities, a continuously updated database compiled by researchers at Arizona State University. One MET equals the energy cost of sitting quietly (approximately 1 kcal/kg/hour).

Accuracy: MET-based estimates have a margin of error of ±15–20%. Heart-rate-based methods (used by fitness trackers) are more accurate for cardio but less reliable for resistance training. Neither method equals laboratory indirect calorimetry.