How the calorie calculator works
First it estimates your basal metabolic rate (BMR) with the Mifflin–St Jeor equation, then multiplies it by an activity factor to get the calories you use in a typical day.
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
| Activity level | Multiply BMR by |
|---|---|
| Little or no exercise | 1.2 |
| Light exercise 1–3 days a week | 1.375 |
| Moderate exercise 3–5 days a week | 1.55 |
| Hard exercise 6–7 days a week | 1.725 |
| Very hard exercise or a physical job | 1.9 |
For a gradual change, the calculator adds or subtracts about 3,500 calories per pound (7,700 per kilogram) spread over a week.
Worked example
A 30-year-old man who weighs 80 kg (176 lb), is 180 cm (5 ft 11 in) tall and exercises moderately:
- BMR: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 calories.
- Daily needs: 1,780 × 1.55 = about 2,759 calories to maintain his weight.
- To lose about 1 lb a week: 2,759 − 500 = about 2,259 calories a day.
Getting the most from the estimate
- Treat it as a starting point. Track your weight for 2 to 4 weeks and adjust by 100 to 200 calories if needed.
- Recalculate after big changes in weight or activity.
- Focus on food quality too. Protein, fibre, fruit and vegetables help you feel full on fewer calories.
Frequently asked questions
How many calories do I need a day?
It depends on your age, sex, size and how active you are. Many adults need somewhere between about 1,600 and 3,000 calories a day. The calculator estimates your own number with the Mifflin–St Jeor equation, which research has found to be one of the more accurate formulas for most adults.
What is BMR?
Basal metabolic rate is the energy your body uses at complete rest to breathe, circulate blood and keep your organs working. Daily activity, exercise and digesting food are added on top, which is why the calculator multiplies BMR by an activity factor.
How many calories should I cut to lose weight?
A common rule of thumb is that eating about 500 fewer calories a day than you use leads to losing about 1 lb (0.45 kg) a week. Real results vary because your body adapts over time. Slow, steady changes are easier to keep up.
Why does the calculator hide some goals?
It hides any target below 1,200 calories a day for women or 1,500 for men, figures commonly cited as the lowest intake that is advisable without medical supervision. Eating less than that makes it hard to get enough nutrients.
Which activity level should I choose?
Choose based on a typical week, not your best one. Most people with desk jobs who exercise a few times a week fit “light” or “moderate”. If you are unsure, pick the lower level and adjust after a few weeks.
Sources
These figures are estimates for healthy adults and are not medical or nutritional advice. If you are pregnant, breastfeeding, have a medical condition, or have a history of disordered eating, talk to a doctor or registered dietitian. Read the full disclaimer and how we check our formulas.