Calorie Calculator

Calorie calculator at a glance#

A calorie calculator estimates how many calories you need each day to maintain, lose, or gain weight. It finds your basal metabolic rate (BMR), the energy you burn at rest, then multiplies it by an activity factor to give maintenance calories. To lose weight, you eat below that number. A deficit of about 500 calories a day works out to roughly 1 pound of fat loss per week.

The calculator uses the Mifflin-St. Jeor equation for BMR. For men, BMR is 10 times weight in kg, plus 6.25 times height in cm, minus 5 times age in years, plus 5. For women, the last term is minus 161 instead of plus 5.

Worked example for a 30-year-old man, 80 kg and 180 cm: BMR is 800 plus 1125 minus 150 plus 5, which is 1780 calories. Multiply by the moderately active factor of 1.55 to get 2759 maintenance calories. Subtract 500 for weight loss and you eat about 2259 calories a day, for roughly 1 pound lost per week.

Enter your age, sex, height, weight, and activity level in the calculator above for your exact maintenance number and deficit. These figures are an estimate: real needs vary with muscle mass, genetics, and how active you really are, so check progress over a couple of weeks and adjust.

How the calorie calculator works#

The calculator finds your basal metabolic rate (BMR) with the Mifflin-St. Jeor equation, then multiplies it by an activity factor to get the calories you burn in a day, your maintenance level. The answer block above shows the formula and a worked example. To lose weight you eat below maintenance, to gain weight you eat above it, and to stay the same you eat at it.

Calorie counting is an estimate, not a precise science. Activity, food labels, and your own metabolism all introduce error, so use the number as a starting point and adjust based on how your weight actually moves over two to three weeks.

Choosing an activity level#

Your activity factor swings the result by hundreds of calories, so pick it carefully. Count both planned exercise and how much you move at work. If you are unsure, choose the lower level: overestimating activity inflates your maintenance number and stalls weight loss. A short bout of 15 to 30 minutes of raised heart rate is light, while an hour of hard effort most days is very active.

Setting a deficit or surplus#

A deficit of about 500 calories a day gives roughly 1 pound of fat loss per week, since a pound of fat holds about 3,500 calories. A safe range is 250 to 500 calories below maintenance; cutting harder than that risks muscle loss, fatigue, and rebound eating. To gain muscle, eat about 200 to 300 calories above maintenance, lift weights, and get enough protein so the surplus builds muscle rather than just fat.

Calories are not the whole story#

Two diets with the same calorie count can affect you differently. Protein and fiber keep you full longer and protect muscle in a deficit, so whole foods like lean meat, fish, eggs, beans, vegetables, and whole grains make a calorie target easier to hit than the same calories from processed snacks. Portion size is the other lever: larger servings raise intake even when the food is healthy.

Frequently asked questions#

How many calories should I eat?#

Most adult women need about 1,600 to 2,400 calories a day and most adult men about 2,200 to 3,000, per the 2020 to 2025 Dietary Guidelines for Americans. Your exact number depends on your size, age, and activity, which is what the calculator estimates.

What is the Mifflin-St. Jeor equation used for?#

It estimates your BMR, the calories you burn at rest. That figure is then multiplied by an activity factor to give your daily maintenance calories.

How does the Katch-McArdle formula differ?#

Katch-McArdle bases BMR on lean body mass instead of total weight, so it can be more accurate if you know your body fat percentage. Mifflin-St. Jeor uses weight, height, age, and sex, and needs no body fat figure.

How big a calorie cut do I need to lose weight?#

About 500 calories a day below maintenance loses roughly 1 pound per week. Larger cuts speed loss but raise the risk of muscle loss and fatigue, so 250 to 500 calories is the usual range.

What is zigzag calorie cycling?#

It alternates higher and lower calorie days while keeping the weekly average at your target. The idea is to avoid a plateau and add flexibility, though the total deficit over the week is what drives weight loss.