Step 1: basal metabolic rate (BMR)
Your basal metabolic rate is the energy your body needs at complete rest to keep the heart beating, the lungs breathing and the organs working. For most people it is 60 to 70 percent of everything they burn in a day. It depends mostly on body size, age and sex, which is why the common formulas use exactly those four values.
The Mifflin-St Jeor equation, published in 1990, is the one dietitians use most today, because studies comparing formulas found it closest to measured values for most adults. Weight is in kilograms, height in centimeters and age in years:
Men: BMR = 10 × weight + 6.25 × height - 5 × age + 5. Women: BMR = 10 × weight + 6.25 × height - 5 × age - 161.
Example: a 30 year old man, 180 cm, 80 kg: 800 + 1,125 - 150 + 5 = 1,780 kcal. A 25 year old woman, 165 cm, 60 kg: 600 + 1,031.25 - 125 - 161 = 1,345 kcal.
Try it here: Calorie Calculator
Open the full tool pageThe Harris-Benedict alternative
The Harris-Benedict equation dates from 1919 and was revised by Roza and Shizgal in 1984. It is still common in textbooks and older apps, and the calculator offers it as an option. For the same man as above it gives about 1,854 kcal, roughly 4 percent more than Mifflin-St Jeor. The difference is typical: Harris-Benedict tends to estimate a little higher for most people.
Men: BMR = 88.362 + 13.397 × weight + 4.799 × height - 5.677 × age. Women: BMR = 447.593 + 9.247 × weight + 3.098 × height - 4.330 × age.
Neither formula knows your body composition. Two people with the same weight burn different amounts if one has much more muscle. For most people the estimate is within about 10 percent of their real needs, which is good enough as a starting point.
Step 2: multiply by your activity level
Total daily energy expenditure (TDEE) adds everything you do on top of resting: walking, work, exercise and digesting food. It is calculated by multiplying BMR by an activity factor. The calculator uses the five standard levels below.
Most people overestimate their activity. Count planned exercise and physically demanding work, not a busy day at a desk. If you are unsure between two levels, choose the lower one and adjust after a few weeks based on what your weight actually does. For the man in the example, sedentary gives 1,780 × 1.2 = 2,136 kcal and moderate gives 2,759 kcal.
| Activity level | Description | Factor |
|---|---|---|
| Sedentary | Desk job, little or no exercise | 1.2 |
| Light | Exercise 1 to 3 days a week | 1.375 |
| Moderate | Exercise 3 to 5 days a week | 1.55 |
| Active | Hard exercise 6 to 7 days a week | 1.725 |
| Very active | Physical job or training twice a day | 1.9 |
Step 3: set a target to lose or gain weight
A kilogram of body fat stores about 7,700 kcal (about 3,500 kcal per pound). A deficit of 500 kcal a day adds up to 3,500 kcal a week, which is roughly 0.45 kg or 1 lb of fat. A deficit of 250 kcal a day gives about half of that. These are the two loss options in the calculator; larger deficits are harder to keep up, make it harder to get enough protein and nutrients, and lead to more muscle loss.
For gaining weight, for example while building muscle, a surplus of 250 to 500 kcal a day keeps fat gain moderate. The calculator shows all five targets side by side, so you can see what each one means for your day.
Real progress is not a straight line. In the first week much of the change is water. As your weight changes, your BMR changes with it, so recalculate every few kilograms. If you eat below about 1,200 kcal (women) or 1,500 kcal (men), the calculator shows a warning, because such low intakes are usually advised only with medical supervision.
Turning calories into macros
Protein and carbohydrates provide 4 kcal per gram and fat 9 kcal per gram. To turn a calorie target into grams, take the share of each macro, multiply by the calories and divide by 4 or 9. With 2,000 kcal and a balanced split of 25 percent protein, 50 percent carbohydrates and 25 percent fat: protein 500 kcal = 125 g, carbohydrates 1,000 kcal = 250 g, fat 500 kcal = 56 g.
The calculator offers three starting points: Balanced (25/50/25), Higher protein (30/40/30), often used when losing weight or training for strength, and Lower carb (30/25/45). None is right for everyone. Health conditions such as diabetes or kidney disease, pregnancy and breastfeeding change what is appropriate, so follow your doctor's or dietitian's advice in those cases.
| Split | Protein | Carbohydrates | Fat | Grams at 2,000 kcal |
|---|---|---|---|---|
| Balanced | 25% | 50% | 25% | 125 g / 250 g / 56 g |
| Higher protein | 30% | 40% | 30% | 150 g / 200 g / 67 g |
| Lower carb | 30% | 25% | 45% | 150 g / 125 g / 100 g |
Limits of any calorie calculator
Formulas describe averages. Genetics, hormones, sleep, medication and how much you move outside the gym all shift your real needs. The best use of a calculator is as a starting point: eat at the suggested level for two to three weeks, weigh yourself under the same conditions a few times a week, and adjust by 100 to 200 kcal if the trend does not match your goal.
The formulas are for adults. Children and teenagers need extra energy for growth, and needs during pregnancy and breastfeeding are different. The calculator and this guide give general information and are not medical or nutrition advice. Your values are calculated in your browser and are not added to the share link or sent anywhere.