Calculator Methodology
Last updated: June 2026
Our calculators use established, published equations rather than proprietary "black box" formulas, so you can see exactly how a result is produced. This page documents the core methods and their limits. All outputs are estimates and starting points, not clinical measurements.
1. BMR — Mifflin-St Jeor
Basal Metabolic Rate (calories burned at complete rest) is calculated with the Mifflin-St Jeor equation, widely regarded as the most accurate general predictive equation for healthy adults:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Try it on the BMR Calculator.
2. TDEE — activity multipliers
Total Daily Energy Expenditure multiplies BMR by an activity factor to account for movement and exercise:
- Sedentary (little/no exercise): × 1.2
- Lightly active (1–3 days/week): × 1.375
- Moderately active (3–5 days/week): × 1.55
- Very active (6–7 days/week): × 1.725
- Extremely active (physical job / 2× training): × 1.9
Choosing the right activity level is the single biggest source of error — most people overestimate. See the TDEE Calculator.
3. Calorie goals — deficit & surplus
Fat-loss and muscle-gain targets adjust TDEE by a sensible percentage rather than an extreme fixed number: typically a 15–25% deficit for fat loss and a 5–15% surplus for lean gaining. We cap deficits to protect muscle and adherence and flag when a target would fall below a reasonable minimum intake.
4. Macros & protein
Protein is set first, in the evidence-supported range of roughly 1.6–2.2 g per kg of bodyweight, higher in a deficit to preserve muscle. Remaining calories are divided between carbohydrate and fat using goal-appropriate splits (for example a higher-protein 35/35/30 split for fat loss, or a 70/25/5 fat-protein-carb split for keto). Protein and carbs are counted at 4 kcal/g, fat at 9 kcal/g.
Use the Macro Calculator and Protein Calculator.
5. Accuracy & limitations
Predictive equations estimate energy needs within roughly 5–10% for most healthy adults, but no formula knows your exact metabolism, NEAT, or how your body responds. Treat every result as a hypothesis: use it for two to three weeks, track your real trend, and adjust. People with medical conditions affecting metabolism (e.g. thyroid disorders) should work with a professional. See our Disclaimer.