How to use the Harris-Benedict Calculator (Basal Metabolic Rate)
The Harris-Benedict equation estimates your Basal Metabolic Rate (BMR) — the number of calories your body burns per day just to keep basic functions running (breathing, circulation, cell repair) while completely at rest. This calculator uses the widely-cited 1984 revision by Roza and Shizgal, which improved on the original 1919 Harris-Benedict formula. Enter your sex, age, weight, height, and activity level to get your BMR, your Total Daily Energy Expenditure (TDEE), and sample calorie targets for mild weight loss or gain. This tool is for education and general planning only — it is not medical advice. Speak with a physician or registered dietitian before making significant changes to your diet, especially if you have a medical condition.
How the math works
- BMR for men: 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years).
- BMR for women: 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years).
- TDEE (Total Daily Energy Expenditure): BMR × an activity multiplier — 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active, 1.725 for very active, or 1.9 for extra active (hard physical training or labor).
- Calorie targets: since roughly 3,500 calories corresponds to about 1 lb (0.45 kg) of body fat, a sustained deficit or surplus of about 500 calories/day relative to TDEE produces roughly 1 lb of change per week.
Common calibration mistakes
- Overestimating activity level — most people who aren't training regularly fall into the sedentary or lightly active categories, not "moderately active."
- Entering height or weight in the wrong unit — double-check the unit selector, since mixing lb with cm (or kg with in) produces a meaningless result.
- Treating BMR as your daily calorie target — BMR is calories at rest only; use the TDEE result (BMR × activity multiplier) for a real-world daily calorie goal.
- Ignoring individual variation — the Harris-Benedict equation is typically accurate to within about ±10% of measured BMR; use it as a starting point and adjust after 2-3 weeks based on actual weight trend.
Frequently Asked Questions
What is the Harris-Benedict equation?
The Harris-Benedict equation estimates your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest — from your sex, weight, height, and age. This calculator uses the 1984 Roza and Shizgal revision: 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).
How is BMR different from TDEE?
BMR is the energy your body needs at complete rest with no activity. Total Daily Energy Expenditure (TDEE) multiplies BMR by an activity factor (1.2 for sedentary up to 1.9 for extra active) to estimate the calories you burn in a full day, including exercise and daily movement.
How accurate is the Harris-Benedict formula?
The revised Harris-Benedict equation is generally accurate to within about 10% of measured BMR for most adults, but the newer Mifflin-St Jeor equation has been shown in several studies to be slightly more accurate for people who are overweight or obese. Both are estimates — individual metabolism can vary.
How many calories should I eat to lose or gain weight?
A deficit of about 500 calories per day below your TDEE typically produces roughly 1 pound (0.45 kg) of weight loss per week, and a 500-calorie surplus produces roughly 1 pound of gain per week, since one pound of body fat corresponds to about 3,500 calories.