How it's calculated
Basal metabolic rate (BMR) uses the Mifflin–St Jeor equation, the most accurate formula for the general population.
Men: BMR = 10·kg + 6.25·cm − 5·age + 5 Women: BMR = 10·kg + 6.25·cm − 5·age − 161
TDEE (Total Daily Energy Expenditure) = BMR × activity multiplier. Your target = TDEE + goal adjustment: −500 kcal to lose weight, +300 kcal to build muscle, or +500 kcal for an aggressive bulk.
| Activity level | Multiplier |
|---|---|
| Sedentary: little or no exercise | 1.2 |
| Light: exercise 1–3 days a week | 1.375 |
| Moderate: exercise 3–5 days a week | 1.55 |
| Active: exercise 6–7 days a week | 1.725 |
| Very active: hard daily training or a physical job | 1.9 |
Worked example
A 35-year-old woman, 165 cm tall and 68 kg, who exercises lightly and wants to lose weight.
- BMR: 10 × 68 + 6.25 × 165 − 5 × 35 − 161 = 680 + 1,031.25 − 175 − 161 = 1,375 kcal.
- TDEE: 1,375.25 × 1.375 = 1,891 kcal a day to maintain her weight.
- Target: 1,891 − 500 = 1,391 kcal a day.
- Protein: 68 kg × 1.8 = 122 g (488 kcal).
- Fat: 25% of 1,391 kcal = 348 kcal, or 39 g.
- Carbs: the remaining 555 kcal, or 139 g.
How activity changes your daily calories
| Activity | Woman, 35, 165 cm, 68 kg | Lose weight | Man, 30, 175 cm, 75 kg | Lose weight |
|---|---|---|---|---|
| Sedentary | 1,650 | 1,200 | 2,039 | 1,539 |
| Light | 1,891 | 1,391 | 2,336 | 1,836 |
| Moderate | 2,132 | 1,632 | 2,633 | 2,133 |
| Active | 2,372 | 1,872 | 2,930 | 2,430 |
| Very active | 2,613 | 2,113 | 3,228 | 2,728 |
The sedentary woman's weight-loss target would be 1,150 kcal, but the calculator raises it to the 1,200 kcal minimum. If your result hits that floor, a smaller deficit or more daily movement is a better lever than eating less.
Macro defaults
Protein is set at 0.8 g per pound of body weight (1.8 g/kg), fat at 25% of calories, carbs fill the rest. These are sensible starting points — adjust based on personal response and goals.
Limitations
Formulas estimate average people. Individual metabolism varies by 10% or more. Adjust up or down based on actual weight change over 2–3 weeks. The calculator never suggests a target below 1,200 kcal per day. The numbers are estimates, not medical advice; if you are pregnant, breastfeeding, under 18 or managing a health condition, ask a doctor or dietitian before changing how you eat.
Making the number work
- Weigh food for a week or two. Portions estimated by eye are often well off, which is the most common reason a deficit seems not to work.
- Use a weekly average weight. Daily weight moves with water and salt, so compare one week's average with the next.
- Recalculate after weight changes. A lighter body burns fewer calories, so update your weight every 4–5 kg (about 10 lb).