How to use it
- Choose US units (pounds, feet and inches) or metric.
- Enter your sex, age, weight and height.
- Pick the activity level that matches a typical week.
- Read the calories that maintain your weight, and the targets to lose or gain about 1 lb (0.5 kg) a week.
How it works
First the calculator estimates your basal metabolic rate (BMR), the energy you burn at complete rest, with the Mifflin–St Jeor equation (Mifflin, St Jeor et al., American Journal of Clinical Nutrition, 1990):
- men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Then it multiplies the BMR by the commonly used activity factor:
| Activity | Factor |
|---|---|
| Sedentary | 1.2 |
| Light (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 | 1.9 |
The targets are the maintenance calories minus or plus 500 kcal a day, the classic estimate for about 1 lb (0.5 kg) a week based on 3,500 kcal per pound (Wishnofsky, 1958). US units are converted exactly: 1 lb = 0.45359237 kg, 1 in = 2.54 cm.
Worked example
A 40-year-old man, 180 lb (81.65 kg), 5 ft 10 in (177.8 cm), who trains 6 days a week:
- BMR = 10 × 81.65 + 6.25 × 177.8 − 5 × 40 + 5 = 1,733 kcal
- maintenance = 1,733 × 1.725 = 2,989 kcal a day
- to lose about 1 lb a week: 2,489 kcal; to gain: 3,489 kcal
Limits and tips
- Equations predict the average person of your size. Muscle mass, genetics, health conditions and medication shift real needs, so check your weight over two or three weeks and adjust by 100–200 kcal.
- The 500-kcal rule overstates long-term loss: as you get lighter you burn less (Hall et al., The Lancet, 2011).
- The calculator is not meant for children, pregnancy or breastfeeding, or for people with eating disorders. For medical conditions, ask a doctor or registered dietitian.