What this calculator gives you
Two numbers, side by side:
- BMR — calories your body burns at complete rest in 24 hours. This is the floor.
- TDEE — BMR × activity multiplier. This is the actual number of calories you burn on a typical day. Use TDEE for any calorie target.
The strip on the right shows TDEE at all five standard activity levels (sedentary → extra active). Click any row to set it as your “selected” level — useful for comparing what changing your activity does to your daily calorie budget.
Which formula to use
- Mifflin-St Jeor (default) — the Academy of Nutrition and Dietetics’ recommendation for adults. Most accurate population-level formula since 1990.
- Harris-Benedict (revised 1984) — still widely cited, but typically overestimates by ~5% for the modern population. Useful if you want to compare against an older app or textbook.
- Katch-McArdle — the most accurate of the three if you have a real body-fat measurement. Uses lean body mass directly, so it’s independent of sex (LBM does the work).
If you pick Katch-McArdle but don’t enter a body-fat percentage, the tool falls back to Mifflin and tells you why.
Privacy
The math runs entirely in your browser via the pure calculateBMR function (src/tools/calculators/bmr.ts in our public repo). Editing any field produces zero network requests — you can verify this in the Network tab. The page doesn’t store inputs in localStorage, doesn’t include them in analytics, and never transmits anything about your body.