Methodology

By Zachary, builder of Mariposas · Reviewed against published exercise-science sources (references) · Last updated June 2026

Our tools use established, published formulas, no proprietary black boxes. Here's exactly what each calculator computes and where the math comes from. Results are estimates; see our medical disclaimer.

Calorie burn (classes & activities)

Calories = MET × body weight (kg) × duration (hours). MET (Metabolic Equivalent of Task) values come from the Compendium of Physical Activities (Ainsworth et al.). We exclude passive "wellness" activities (sauna, cold plunge, massage) from calorie pages because reporting a calorie burn for sitting still would be misleading.

Energy needs (BMR & TDEE)

BMR uses the Mifflin-St Jeor equation (the most accurate for the general population), with Harris-Benedict and Katch-McArdle offered as alternatives. TDEE = BMR × an activity factor (1.2-1.9).

Strength (1RM)

One-rep-max estimates use the Epley (1RM = w × (1 + reps/30)), Brzycki, Lombardi, Lander and O'Conner formulas. Accuracy drops above ~10 reps, which we flag on the tool.

Running (pace & race prediction)

Pace = time ÷ distance. Race-time prediction uses Riegel's formula (T₂ = T₁ × (D₂/D₁)^1.06). We use Riegel rather than proprietary VDOT tables so the math is transparent and verifiable.

Body composition

Body-fat estimates use the US Navy circumference method and the Jackson-Pollock skinfold equations with the Siri conversion. BMI = kg/m². These are population estimates and are not diagnostic.

Heart-rate zones

Max HR via Tanaka (208 − 0.7 × age) by default; zones via the Karvonen heart-rate-reserve method when resting HR is provided.

How we check this

Every calculator is implemented straight from the published formula above and verified against worked examples from the original papers and against other reputable calculators before it ships, if our number disagrees with the source, we fix the implementation, not the disclaimer. The training guides are written by the person who builds and trains with Mariposas day to day, and any non-obvious claim (training volume, protein intake, progression rate) is cited inline to a published source you can check. We don't claim medical or dietetic credentials we don't have, where a topic needs a professional, we say so and link the medical disclaimer. Found a number that looks off? Tell us and we'll re-check it against the source.

Full source list on our references page.