Calorie Calculator

How the Calorie Calculator Works — and How to Use Your Number

Calories are units of energy. Every food you eat contains them, every physical activity you do burns them, and your body is quietly using them every second of the day — even while you're asleep. Your “daily calorie needs” is an estimate of how much energy your body uses in 24 hours, and it's the foundation for just about every nutrition decision you'll ever make. Eat roughly what you burn, and your weight stays steady. Eat less, and you'll lose weight. Eat more, and you'll gain it. Our calculator uses well-established formulas to figure out your personal number, factoring in your age, sex, height, weight, and how active you are.

The formula behind it

We use the Mifflin-St Jeor equation, which is the formula the American Dietetic Association recommends for most adults. It estimates your Basal Metabolic Rate (BMR) — the calories your body would burn if you did nothing all day except lie still. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. Once we have your BMR, we multiply it by an “activity factor” ranging from 1.2 (sedentary) to 1.9 (extremely active). The result is your Total Daily Energy Expenditure (TDEE) — the number you see on screen. It's the average amount of energy your body uses in a typical day, given your lifestyle.

What your result means

Your TDEE is your maintenance number. Eat that many calories per day and your weight should stay roughly the same. For weight loss, the standard guidance is to create a deficit of about 500 calories per day, which produces roughly one pound of fat loss per week. That means eating TDEE − 500. For weight gain, add 300–500 calories per day — a larger surplus mostly leads to fat gain rather than muscle, so slower is better. Keep in mind that a deficit should never push you below about 1,200 calories per day for women or 1,500 for men without medical supervision; going too low is unsustainable and can harm your metabolism and health.

Activity levels, decoded

The biggest source of error in any calorie calculator is the activity factor, because it's self-reported. “Sedentary” means a desk job and little to no exercise. “Lightly active” means light exercise one to three days per week. “Moderately active” means moderate exercise three to five days per week. “Very active” means hard exercise six to seven days per week. “Extremely active” is for athletes training twice a day or people with physical jobs. Most people overestimate their activity level — if you're unsure, choose one level lower than you think. It's better to underestimate and adjust upward than to overestimate and wonder why the scale isn't moving.

Limitations to keep in mind

Calorie calculators give you an estimate, not a precise measurement. The Mifflin-St Jeor equation is typically accurate to within about 10% for most people, but individual metabolism varies widely. Two people the same age, height, and weight can have TDEEs that differ by 300 calories or more, due to genetics, muscle mass, gut bacteria, hormones, and other factors. Your real TDEE can only be measured precisely in a lab. Use the calculator as a starting point, then track your actual intake and weight for two to three weeks. If your weight isn't moving the way you want, adjust your target by 100–200 calories and give it another two weeks. That feedback loop is more accurate than any formula.