BMR calculator for adults — Mifflin St Jeor and Katch–McArdle
Calculate basal metabolic rate
BMR calculator for adults: methods, inputs, accuracy and next steps
What the BMR calculator shows
This BMR calculator estimates your basal metabolic rate using two respected methods. Mifflin–St Jeor is the default because it performs well in modern validation studies for typical adults. If you provide body fat percentage, the tool also computes Katch–McArdle using lean body mass. You will see both results when possible, plus a simple energy-per-hour view and practical guidance to interpret the numbers.
Which inputs matter most
Age, sex, height and weight are required for the Mifflin–St Jeor equation. Body fat percentage is optional but can personalize results via Katch–McArdle. If you do not know body fat, you can skip it—your Mifflin result will still be useful for planning. Accurate measurements improve reliability: measure height without shoes, use a recent morning body weight, and round to the nearest half unit rather than guessing.
How to read your result
BMR reflects energy your body uses at complete rest for essential functions such as breathing and circulation. Daily needs are higher than BMR because you move, digest food, and perform tasks. If you are using this figure to guide nutrition, consider sending it to a total daily energy (TDEE) calculator that layers in activity. If the two methods differ by less than 10%, they are broadly consistent; when the gap is larger, trust the method that best matches your context—Katch–McArdle for accurate body fat measurements, Mifflin–St Jeor otherwise.
Improving estimate quality
- Use consistent morning weigh-ins after bathroom and before breakfast.
- Recalculate if weight changes by more than 2–3% or body fat shifts meaningfully.
- If strength training increased lean mass, Katch–McArdle may track changes better.
- For athletes or clinical cases, indirect calorimetry is the gold-standard measurement.
Practical next steps
Most users combine BMR with activity multipliers to plan maintenance calories, a modest calorie deficit for weight loss, or a small surplus for lean gain. You can move from this tool to the TDEE & Macro Calculator to apply activity level, protein targeting, and macro splits. Track weekly averages and adjust 5–10% at a time based on trends rather than single-day fluctuations.
Limits and caveats
- Equations estimate population averages; individual metabolism varies with sleep, hormones, medications and past dieting.
- Body fat tools vary widely; DEXA and reliable skinfolds beat visual guesses or cheap bioimpedance.
- Teenagers, pregnancy, and certain medical conditions require specialist guidance beyond generic equations.
BMR calculator FAQs
What is a normal BMR?
BMR varies with size and composition. Many adult results fall between 1,200–2,100 kcal/day, but smaller or larger bodies can sit outside this range.
Which method should I use?
Use Mifflin–St Jeor by default. If you know body fat from a reliable method, also review Katch–McArdle and compare.
Does BMR equal maintenance calories?
No. BMR reflects rest only. Maintenance needs are higher and depend on activity. Use a TDEE calculator to estimate daily totals.
How often should I recalculate?
Update after notable weight or body fat changes, or every few months if your training or job activity shifts.
Is body fat required?
No. It is optional and only needed for the Katch–McArdle calculation.