How this calorie calculator works
First it estimates your basal metabolic rate (BMR), the energy your body uses at rest, with the Mifflin–St Jeor equation. For women that is 10 × weight in kg + 6.25 × height in cm − 5 × age − 161; for men the last number is +5 instead. Mifflin–St Jeor is widely used because it tends to be closer to measured energy use than older formulas.
BMR is then multiplied by an activity factor, from 1.2 for a desk job with little exercise up to 1.725 for hard training most days. The result is your total daily energy expenditure (TDEE), or maintenance calories: eat about this much and your weight should stay roughly the same.
Calories to lose weight
To lose fat you need to eat less than your maintenance. Thrive Fit starts with 300 calories below maintenance, which is gentle enough to keep up for months. Many people use 500 below for faster progress. Bigger deficits tend to bring more hunger, less energy for workouts and more muscle loss, so they are harder to stick to. Read more in how many calories to eat to lose weight.
Protein, carbs and fat
Protein is set from your body weight: 1.8 g per kg when losing weight or building strength, and 1.5 g per kg to maintain. Higher protein helps you feel full and protects muscle in a deficit. Fat is set at 28% of calories, and carbs make up the rest to fuel your training.
Use your number
- Track what you eat for two to three weeks and weigh yourself at the same time each morning.
- Look at your weekly average weight, not single days, which move with water and salt.
- No change after three weeks? Lower your target by 100–200 calories, or add more daily movement.
- Need meals that hit your number? Browse the free 7-day meal plans.
In the Thrive Fit app your target is set for you during setup, and you can log meals with a photo to see what is left for the day. Also see the BMI calculator and our health sources.
