Formula and Method for the Harris-Benedict BMR Calculator
The Harris-Benedict equation estimates your Basal Metabolic Rate (BMR) — the number of calories your body burns at complete rest just to keep essential functions running, such as breathing, circulation, and cell repair. This calculator uses the revised (1984) Harris-Benedict equation, recalculated by Roza and Shizgal from a larger sample than the original 1919 version. Multiplying BMR by an activity multiplier gives your Total Daily Energy Expenditure (TDEE) — roughly how many calories you burn in a typical day. This tool is for education and planning only and does not replace individualized advice from a registered dietitian or physician.
How the calculation works
Enter your sex, age, weight, height, and typical activity level. The calculator converts weight and height to metric units (kilograms and centimeters) if needed, then applies the revised Harris-Benedict equation. For men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years). For women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years). TDEE is then BMR multiplied by an activity factor from 1.2 (sedentary) to 1.9 (extremely active).
Common mistakes
- Confusing BMR with TDEE: BMR is calories at complete rest only — it does not include walking, exercise, or digestion. TDEE is the number to use for daily calorie targets.
- Overestimating activity level: most people who exercise a few times a week are "lightly active," not "very active." Choosing too high a multiplier inflates TDEE and calorie targets.
- Double-counting exercise calories: if you already selected an active multiplier, don't also add back calories burned from a fitness tracker — that double-counts the same activity.
Using your results to set calorie targets
A deficit of roughly 500 kcal/day below TDEE typically produces about 1 lb (0.45 kg) of weight loss per week; a 500 kcal/day surplus produces roughly 1 lb of gain per week. Treat these numbers as a starting point — real-world results vary by 10–15% due to individual metabolism, and intakes below about 1,200 kcal/day (women) or 1,500 kcal/day (men) should only be pursued under medical supervision. This calculator is not appropriate for children, pregnant or breastfeeding people, or anyone with a diagnosed metabolic or eating disorder — consult a physician or registered dietitian in those cases.