Quick answer: Daily calorie needs are your basal metabolic rate multiplied by an activity factor. The Mifflin-St Jeor equation estimates the basal rate: for men 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5, and for women the same with −161 at the end. A 30-year-old man who is 180 cm and 80 kg and exercises 3 to 5 days a week needs about 2,759 calories to maintain his weight.
Your body burns calories even at rest, to keep your heart beating, your lungs working and your organs running. That resting figure is your basal metabolic rate (BMR). Add the calories you burn moving around and exercising, and you get your total daily energy expenditure (TDEE), which is roughly the amount you need to eat to stay at the same weight.
To lose weight you eat less than your TDEE, and to gain you eat more. The calculator shows several targets so you can pick a pace that suits you. Slow and steady is easier to keep up than a crash diet.
The formula behind the result
This calculator uses the Mifflin-St Jeor equation, which studies have found to be among the more accurate estimates of resting energy use for most adults.
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
TDEE = BMR × activity factor (1.2 to 1.9)
About 7,700 kcal is often used as the energy in a kilogram of body fat (3,500 kcal per pound), so a daily gap of 550 kcal works out to roughly 0.5 kg a week. In practice, weight loss rarely follows the arithmetic exactly, because your metabolism and habits adapt.
A worked example
Example. A 30-year-old man who is 180 cm tall and weighs 80 kg has a BMR of 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 kcal. With moderate exercise (× 1.55) he needs about 2,759 kcal a day to maintain his weight, and about 2,209 kcal to lose roughly 0.5 kg a week.
Real-world example
A 35-year-old woman who is 165 cm tall and weighs 60 kg has a basal rate of 1,295 calories. With light exercise (× 1.375) she needs about 1,781 calories a day to stay the same weight. Eating around 250 to 500 calories below that would be a moderate, sustainable way to lose weight slowly.
How activity changes the total
| Activity level | Multiplier | Calories for the 30-year-old man |
|---|---|---|
| Sedentary: little or no exercise | 1.2 | 2,136 |
| Light: exercise 1 to 3 days a week | 1.375 | 2,448 |
| Moderate: exercise 3 to 5 days a week | 1.55 | 2,759 |
| Very active: exercise 6 to 7 days a week | 1.725 | 3,070 |
| Extra active: hard training or a physical job | 1.9 | 3,382 |
His basal metabolic rate is 1,780 calories. Multiplying by the activity factor gives the calories that keep his weight steady.
Common mistakes to avoid
- Picking an activity level that is too high. Most people who sit at work and exercise a few times a week belong in “light” or “moderate”.
- Cutting calories too far. Very low intakes are hard to keep up and can cause health problems, so change your intake gradually and speak to a professional about big changes.
- Expecting the estimate to be exact. Real needs differ between people by 10 to 15%, so treat the number as a starting point and adjust from your results over a few weeks.
Go deeper: read our guide BMI Explained: Categories, Limits and Alternatives.
Frequently asked questions
How accurate is a calorie calculator?
It gives a good starting estimate. Individual needs can differ by 10 to 15% from the formula. Track your weight for two to three weeks and adjust the target based on what actually happens.
What is the difference between BMR and TDEE?
BMR is the energy your body uses at complete rest. TDEE includes daily movement and exercise on top of that, so it is the figure that matters for maintaining weight.
How fast is it safe to lose weight?
Many health organizations suggest around 0.5 to 1 kg (1 to 2 lb) a week for most people. Very low calorie targets should only be followed under medical supervision. The calculator shows figures in red if they fall below commonly advised minimums.
Should I eat back the calories I burn exercising?
The activity level already accounts for your usual exercise. If you add extra workouts, you can increase your intake a little, but many people overestimate the calories burned in a workout.
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Sources and further reading
- Basal metabolic rate, including the Mifflin-St Jeor equation (Wikipedia)
- Mifflin MD, St Jeor ST, et al. “A new predictive equation for resting energy expenditure in healthy individuals.” American Journal of Clinical Nutrition, 1990
- Dietary Guidelines for Americans (U.S. Department of Agriculture and HHS)
Formulas on this page are checked by automated tests against independent references. See how we test our tools.