About this tool
This calorie calculator estimates how many calories you burn in a day and how many to eat to reach a goal. From your sex, age, height, weight, and activity level it computes basal metabolic rate (the energy your body uses at complete rest) with the Mifflin-St Jeor equation, shows the revised Harris-Benedict figure for comparison, multiplies by an activity factor to get total daily energy expenditure (TDEE, your maintenance calories), and then applies a daily deficit or surplus for the goal you choose: maintain, lose 0.25, 0.5, or 1 kg a week, or gain 0.25 or 0.5 kg a week. It warns when a target falls below the commonly cited safety floors of 1,200 kcal a day for women and 1,500 for men, splits the target into protein, carbohydrate, and fat grams using a 30/40/30 ratio, and lists maintenance calories at every activity level so you can see what changes if you move more. It is for adults planning a diet or a training block who want a defensible starting number rather than a guess.
How it works
Basal metabolic rate uses the Mifflin-St Jeor equation (1990), which validation studies have found the most accurate of the common formulas for healthy adults: men BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; women BMR = 10 × weight + 6.25 × height − 5 × age − 161. For comparison the page also computes the revised Harris-Benedict equation (Roza and Shizgal, 1984): men 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age; women 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age. Maintenance calories (TDEE) multiply BMR by a physical activity level: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extra active. Goal targets add or subtract calories on the rule that one kilogram of body fat holds about 7,700 kcal, so losing 0.5 kg a week needs a deficit of roughly 550 kcal a day and 1 kg a week about 1,100. Macros use 4 kcal per gram of protein and carbohydrate and 9 kcal per gram of fat.
Frequently asked questions
How accurate are these calorie numbers?
Mifflin-St Jeor predicts measured resting energy expenditure to within about 10 percent for roughly 70 percent of healthy adults, so treat the result as a starting estimate with a margin of a couple of hundred calories. Muscle mass, genetics, thyroid function, and how honestly the activity level is chosen all move the true figure. The usual approach is to eat at the calculated target for two to three weeks, track weight, and adjust by 100 to 200 kcal in whichever direction the scale suggests.
Which activity level should I pick?
Sedentary (1.2) means a desk job and little deliberate exercise. Lightly active (1.375) is light exercise or sport one to three days a week. Moderately active (1.55) is moderate exercise three to five days a week. Very active (1.725) is hard exercise six or seven days a week, and extra active (1.9) is hard daily training plus a physical job or twice-a-day sessions. Most people overestimate; if in doubt pick the lower level and adjust after a few weeks of tracking.
Why does the calculator warn below 1,200 or 1,500 calories?
Very low intakes make it hard to meet protein, vitamin, and mineral needs, tend to cost muscle as well as fat, and are difficult to sustain. Dietary guidance in the US and UK commonly cites 1,200 kcal a day for women and 1,500 for men as the floor for unsupervised dieting. A smaller deficit over a longer period usually works better; anything below those floors should only be done with medical supervision.
Is 7,700 calories per kilogram of fat correct?
It is the standard planning figure: body fat tissue is about 87 percent lipid at roughly 9 kcal per gram, which gives close to 7,700 kcal per kilogram (3,500 per pound). In practice weight loss is not perfectly linear because the body adapts, some of the loss is water and lean tissue, and energy expenditure falls as weight drops, so real losses are usually slower than the rule predicts after the first few weeks. Recalculate your target as your weight changes.