How the calorie calculator works
Your daily calorie needs have two main parts: the energy your body burns at rest and the energy you burn moving around. This calculator first estimates your resting needs with the Mifflin-St Jeor equation, which research has found to be the most accurate of the common formulas for healthy adults. For men it is 10 × weight in kg + 6.25 × height in cm − 5 × age + 5. For women the final term is −161 instead of +5.
That resting figure is then multiplied by an activity factor, from 1.2 for a desk job with little exercise up to 1.9 for heavy training or physical labor. The result is your maintenance calories, the amount that should keep your weight stable. A 35-year-old man who is 175 cm, 75 kg and moderately active needs about 1,674 × 1.55 ≈ 2,594 kcal a day.
Calories for weight loss and gain
A pound of body fat stores roughly 3,500 kcal, so a daily deficit of 500 kcal leads to about one pound of loss per week, and a 1,000 kcal deficit to about two pounds. In metric, half a kilogram is roughly 3,850 kcal, so we use a 550 kcal daily deficit for 0.5 kg per week. The calculator lists mild, standard and fast loss targets, along with two gain targets for people building muscle or recovering from illness.
Real weight change is rarely this tidy. Early in a diet you lose water and stored carbohydrate, which makes the scale drop quickly, and as you get lighter your maintenance calories fall too. Recalculate every 4 to 6 weeks with your new weight to keep the target accurate.
Choosing an honest activity level
Most people overestimate how active they are. If you exercise three times a week but sit for the rest of the day, the lightly active or moderately active setting is usually closer than very active. Steps matter too: someone who walks 10,000 steps a day burns several hundred more calories than someone who walks 3,000, even without formal exercise. When in doubt, start one level lower and adjust based on how your weight responds over two or three weeks.
Safe minimums and when to get help
Very low calorie intakes can leave you short of protein, vitamins and minerals, and they are hard to stick with. General guidance is not to go below about 1,500 kcal a day for men or 1,200 kcal for women without supervision, and the calculator shows a warning when a target falls under those numbers. People who are pregnant or breastfeeding, have diabetes, have a history of eating disorders, or take medication that affects appetite or metabolism should speak to a doctor or registered dietitian before changing how much they eat.
Calorie targets work best alongside food quality. Prioritizing protein, vegetables, fruit and whole grains makes it easier to feel full on fewer calories and helps you keep muscle while you lose fat.
Frequently asked questions
How many calories should I eat to lose weight?
A deficit of about 500 kcal below your maintenance calories leads to roughly 1 lb (0.45 kg) of loss per week. Use the “weight loss” row in your results as a starting point.
Which formula does this calculator use?
It uses the Mifflin-St Jeor equation for resting metabolic rate, multiplied by a standard activity factor.
Why am I not losing weight at the suggested calories?
Activity is often overestimated and portions underestimated. Track your intake carefully for two weeks, choose a lower activity level, and recalculate as your weight changes.
Is it safe to eat 1,200 calories a day?
For some smaller women it can be, but it is generally the lowest intake recommended without medical supervision. Men should usually stay above about 1,500 kcal.