The revised Harris-Benedict formula
The equation uses weight, height, age and sex, with different constants for men and women. Weight is in kilograms, height in centimeters, age in years.
Men run higher for the same size, mostly because of greater muscle mass. Every term after the constant nudges the result: more weight and height raise BMR, more age lowers it.
From BMR to daily calories: activity multipliers
BMR is what you burn at rest. Multiply it by an activity factor to get total daily energy expenditure (TDEE) — the calories that actually maintain your weight.
| Activity level | Roughly | Multiplier |
|---|---|---|
| Sedentary | Desk job, no exercise | × 1.2 |
| Lightly active | 1–3 days a week | × 1.375 |
| Moderately active | 3–5 days a week | × 1.55 |
| Active | 6–7 days a week | × 1.725 |
| Very active | Hard daily training or physical job | × 1.9 |
To lose weight, eat 300–750 calories below TDEE; to maintain, eat at it. It is generally advised not to drop below your BMR for long.
What the number does and does not tell you
- It is an estimate — formulas land within about 10 to 20 percent of your true rate. Track your weight over two to four weeks and adjust the calorie target to what actually happens.
- Harris-Benedict vs Mifflin-St Jeor — Harris-Benedict tends to read a bit high for modern populations; Mifflin-St Jeor is the current default in dietetics. Both are close for most people.
- Muscle matters more than exercise — BMR rises with lean mass, not directly with a workout. The calories a session burns come mostly from the session itself, not a lasting BMR bump.
Common questions
What does the Harris-Benedict equation calculate?
It estimates your basal metabolic rate, the calories your body burns at complete rest to keep the heart, brain, lungs and other basics running. BMR is 60 to 75 percent of total daily calories for most people.
How do I go from BMR to how much I should eat?
Multiply BMR by an activity factor, from 1.2 for a sedentary desk job up to 1.9 for daily intense training. That gives total daily energy expenditure. Eat below it to lose weight, at it to maintain, above it to gain.
Is Harris-Benedict accurate?
It is a solid estimate but tends to run a little high for modern bodies, by roughly 5 to 15 percent. The Mifflin-St Jeor equation is generally more accurate today. Treat any formula as a starting point and adjust from real results over a few weeks.
