About MyBodyMath
MyBodyMath is a small, independent site that does one thing: it turns the published equations of nutrition and exercise science into calculators you can actually use, and then explains what the number means.
Why this site exists
Most people who want to change their body composition hit the same wall in their first week. They read that they need a calorie deficit, they search for a calculator, and they get a number with no context. Is 2,140 a lot? Is it accurate? What happens if it’s wrong? Should they subtract 500 from it, or 20 percent, and why do different sites say different things?
The calculators themselves are not the hard part — every formula on this site is published, peer-reviewed, and freely available. The hard part is knowing which formula applies to you, how much error it carries, and what to do when the number and the scale disagree. That gap is what MyBodyMath was built to fill. Every calculator here shows you the equation it used, names the study it came from, states its known margin of error, and tells you what to do next.
Who writes this
MyBodyMath is written and maintained by a one-person editorial team based in Canada.
We are deliberately clear about what we are not: nobody here is a physician, a registered dietitian, or a certified clinician. We do not give personalised medical advice and we never will. What we do is read the primary literature carefully, implement the equations faithfully, show our sources, and write plainly about uncertainty. Where the research is genuinely contested — and in nutrition it often is — we say so rather than picking the answer that makes for a tidier headline.
If you are managing a medical condition, pregnant, under 18, recovering from an eating disorder, or taking medication that affects appetite or metabolism, the numbers on this site are not a substitute for a conversation with your doctor or a registered dietitian. Read our medical disclaimer for the full picture.
What we build with
Every calculator on the site is a direct implementation of a published equation. We do not invent formulas, blend them into proprietary scores, or adjust them to produce friendlier results. The core equations are:
| Calculator | Equation used | Source |
|---|---|---|
| TDEE | Mifflin-St Jeor × activity factor | Mifflin et al., 1990 |
| BMR | Mifflin-St Jeor and revised Harris-Benedict | Mifflin 1990; Roza & Shizgal 1984 |
| Macros | Protein per kg bodyweight, fat floor, carbs as remainder | Morton et al., 2018; ISSN position stands |
| Body fat | US Navy circumference method; BMI-based estimate | Hodgdon & Beckett, 1984 |
| Ideal weight | Robinson, Miller, Devine, Hamwi | Devine 1974; Robinson 1983; Miller 1983 |
| One rep max | Epley, Brzycki, Lombardi | Epley 1985; Brzycki 1993 |
| Calories burned | MET × weight × duration | Ainsworth et al., Compendium of Physical Activities |
Our How We Calculate page walks through each equation in full, including the arithmetic, so you can check our work by hand.
How the site makes money
MyBodyMath is free and carries display advertising. We do not sell supplements, we do not run affiliate links inside calculator results, and we do not take money to recommend a product or a diet. Advertising is the only revenue on the site, which means our incentive is to be the page you come back to rather than the page that sells you something once.
We also do not require an account. Calculations run entirely in your browser — the numbers you type are never sent to or stored on our servers. See our privacy policy for details on what is and is not collected.
Corrections and contact
If you find an arithmetic error, a misquoted study, or a claim that the research does not support, we want to hear about it and we will fix it. Corrections are logged with a date on the affected page. Write to us through the contact page — our standards for what gets published and how we handle mistakes are set out in our editorial policy.
Last updated September 14, 2026.