Methodology
Every calculator on CalcFitLab uses a published, peer-reviewed equation. We cite the source on each tool's page and do not tune the formulas. This page explains how the tools are built, reviewed and kept current.
Formulas we use
- TDEE uses the Mifflin-St Jeor equation (Am J Clin Nutr, 1990) with standard activity multipliers from 1.2 to 1.9.
- Macros convert calories to grams with the Atwater factors: 4 kcal/g protein and carbs, 9 kcal/g fat.
- One-rep max reports the Epley and Brzycki estimates and their average.
- BMI uses the WHO definition (kg/m²) with the WHO adult cut-offs.
- Body fat uses the U.S. Navy circumference method (Hodgdon & Beckett, 1984).
- BMR reports Mifflin-St Jeor, the revised Harris-Benedict (Roza & Shizgal, 1984) and, with a body-fat figure, Katch-McArdle.
- Calorie deficit uses ~7,700 kcal per kg of body weight and flags plans faster than 1% of body weight per week.
- Walking calories multiply MET values from the 2011 Compendium of Physical Activities by body weight and time.
- Heart-rate zones use the Tanaka max heart rate (208 - 0.7 x age) and the Karvonen heart-rate-reserve method.
How we review
The CalcFitLab editorial team checks the formulas and copy against the cited sources: NHS, WHO, ACSM and the original peer-reviewed papers. We re-check sources and update the tools when guidance changes.
Limits
These tools give estimates for healthy adults and do not replace medical advice. Speak to a qualified professional before changing your diet or training.
Frequently asked questions
This page explains where every number on CalcFitLab comes from: which equation each calculator uses, the source it is drawn from, and when it was last reviewed. Nothing here is a black box — each formula is named so you can check it. The questions below cover how to read the results and how far to trust them.
How often are the formulas reviewed?
On a fixed schedule, and the last review date is shown on this page. When a source body updates a guideline or a better-validated equation becomes standard, we revise the tool and re-date it rather than leaving old numbers in place.
Why do different calculators give different numbers?
Because they use different equations. A TDEE from Mifflin–St Jeor and one from Harris–Benedict can differ by a hundred calories, and two body-fat methods can disagree by several points. We pick the equation with the best validation for a general audience and name it, so you know which one produced your result.
Are these results medical advice?
No. The calculators give population-level estimates for planning training and nutrition. They do not account for medical conditions, medication or individual metabolism, and they are not a substitute for advice from a doctor or registered dietitian.
What sources do you cite?
Each formula is tied to a named source: the NHS and WHO for health thresholds, the ACSM for exercise science, and the original peer-reviewed papers for equations like Mifflin–St Jeor, Epley and the Navy body-fat method. The list above links each one.
How should I interpret an estimate?
As a starting point, not a verdict. Use it to set an initial target, then adjust from what actually happens over two to three weeks — real weight change, performance and how you feel matter more than the first number the tool prints.
Who writes and checks this content?
The CalcFitLab editorial team, part of the team behind the Trainera coaching platform. Every formula comes from a published, peer-reviewed or official source cited on the page. The methodology, sources and review date are published so the work can be checked rather than taken on trust.