How this calculator works
It estimates two numbers: what your body burns at rest, your basal metabolic rate (BMR), and what you burn on a normal day once activity is included, your total daily energy expenditure (TDEE). Then it adjusts for your goal and suggests how to split those calories between protein, fat and carbs.
The Mifflin-St Jeor equation
For BMR, in US units:
- Men:
4.536 × lb + 15.88 × in − 5 × age + 5 - Women:
4.536 × lb + 15.88 × in − 5 × age − 161
Published in 1990, it has held up better in studies than the older Harris-Benedict equation, and it’s the one the Academy of Nutrition and Dietetics recommends for healthy adults.
From BMR to your daily calories
TDEE is your BMR multiplied by an activity factor:
| Activity level | Factor |
|---|---|
| Sedentary: desk job, no exercise | 1.2 |
| Light: exercise 1–3 days a week | 1.375 |
| Moderate: 3–5 days a week | 1.55 |
| Active: 6–7 days a week | 1.725 |
| Very active: physical job or two sessions a day | 1.9 |
Be honest here: most people overestimate how active they are, and choosing one level too high adds several hundred calories a day.
Two examples
A 30-year-old man, 5′11″ and 176 lb, moderately active. His BMR is about 1,780 calories and his maintenance, 2,760. To lose fat he’d aim for about 2,208 a day, split into roughly 144 g of protein, 61 g of fat and 270 g of carbs.
A 35-year-old woman, 5′4″ and 140 lb, sedentary. Her BMR is about 1,315 calories and her maintenance, 1,578. Adding three days of exercise a week raises that noticeably, which is often an easier lever than eating less.
Losing, maintaining or gaining
- Lose fat: 20% below maintenance. It’s enough to see steady progress without feeling starved, and it never drops below your BMR.
- Maintain: your TDEE as is.
- Build muscle: a modest surplus, 15% above maintenance. Eating far more doesn’t build muscle faster; it mostly adds fat.
The old rule that a pound of fat equals 3,500 calories is only a rough guide: as you lose weight your body burns less, so progress slows. Recalculate every 10 pounds or so.
It’s an estimate, not a prescription
Two people with the same numbers can burn 300 calories a day apart. Treat the result as a starting point, track your weight for two or three weeks and adjust. If you have a medical condition or are pregnant, talk to a registered dietitian or your doctor. To see where your weight sits today, try the BMI calculator.