Calorie calculator
Find out how many calories to eat a day, plus your protein, carbs and fat. It uses the same math as the plan in the CalSimple app.
Updated October 11, 2026
How many calories should I eat a day?
It depends on your body, how active you are and your goal. The calculator first works out your maintenance calories: roughly what you burn in a day, so eating that much keeps your weight about the same. To lose weight it takes calories away from that number; to gain, it adds them.
Treat the result as a starting point. Eat close to it for two or three weeks, weigh yourself about once a week, and adjust by 100 to 200 kcal if your weight isn’t moving the way you planned.
How the calculator works
- Resting energy. It uses the Mifflin-St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age, then + 5 for men or − 161 for women. “Other” uses the midpoint of the two.
- Activity. That number is multiplied by 1.375 for 0–2 workouts a week, 1.55 for 3–5, or 1.725 for 6 or more. The result is your maintenance calories.
- Your goal. A kilogram of body weight is counted as about 7,700 kcal, so losing 0.5 kg a week means eating about 550 kcal a day less than maintenance (7,700 × 0.5 ÷ 7). Gaining works the same way in reverse.
- A floor. The daily target never goes below 1,200 kcal (1,500 for men). If your pace would take you lower, pick a slower one.
- Macros. Protein is 1.8 g per kg of body weight, up to 35% of your calories. Fat is 27% of calories. Carbs fill the rest.
- Water. 35 ml per kg of body weight, kept between 1.5 and 4 liters a day.
How fast should I lose weight?
Slower is easier to keep. The CDC says people who lose about 1 to 2 pounds a week (roughly 0.5 to 1 kg) are more likely to keep the weight off. The pace slider goes from 0.1 to 1.5 kg a week, like the app’s, but the middle of that range suits most people.
Common questions
Is this a TDEE calculator?
Yes. TDEE (total daily energy expenditure) is what the calculator calls maintenance: your resting energy times your activity level. Pick “Maintain” to see it as your target.
How accurate is it?
Any formula is an estimate. Two people with the same numbers can burn a few hundred calories a day more or less. Your weight trend over a few weeks is the real test, which is why the app puts your weigh-ins next to your plan.
Can I change the targets in the app?
Yes. CalSimple asks the same questions when you start, shows these targets, and lets you change any of them whenever you like. See how logging works.
The calculator gives an estimate for healthy adults and isn’t medical advice. Teens, and anyone who is pregnant, breastfeeding or has a health condition, should talk to a doctor or dietitian before changing how they eat.