Every calorie-counting plan, from a simple diet app to a coach's meal plan, starts from the same number: how many calories your body burns in a day. That number is your Total Daily Energy Expenditure, or TDEE, and understanding how it's built helps explain why two people who look similar can need very different amounts of food.
The four pieces of TDEE
TDEE isn't one thing, it's a sum of several components. The largest by far is your basal metabolic rate (BMR), the energy your body burns simply staying alive: breathing, circulating blood, maintaining body temperature, repairing cells. For most people, BMR accounts for somewhere between 60 and 75 percent of total daily burn.
On top of BMR sits the thermic effect of food, the energy your body spends digesting and processing what you eat (roughly 10 percent of intake), non-exercise activity thermogenesis or NEAT (fidgeting, walking around, everyday movement that isn't structured exercise), and finally, deliberate exercise.
Why BMR varies so much between people
Muscle tissue burns more energy at rest than fat tissue does, which is a major reason BMR varies so widely between individuals of the same height and weight. Age plays a role too: BMR tends to decline gradually as we get older, partly because muscle mass naturally decreases over time. Sex matters as well, since men typically carry more muscle mass than women at the same body weight, which is reflected in most BMR formulas, including the Mifflin-St Jeor equation used in our BMR calculator.
Turning TDEE into a plan
Once you know your TDEE, the math for weight change is straightforward in principle: eat below it consistently and you'll lose weight over time, eat above it and you'll gain. A deficit of roughly 500 calories a day, sustained over a week, works out to about a pound of fat loss weekly, since a pound of body fat holds approximately 3,500 calories.
In practice, TDEE estimates from formulas are a starting point, not a guarantee. Individual metabolism varies by up to 10-15 percent from the formula's prediction, and factors like sleep, stress, and how accurately you're tracking food intake all affect real-world results. The sensible approach is to start from an estimated number, track your actual weight trend over two to three weeks, and adjust the target up or down based on what you observe.
Where to start
Our calorie calculator estimates your TDEE using the Mifflin-St Jeor formula and gives you targets for maintaining, losing, or gaining weight. If you want your calories broken down into protein, carbs, and fat as well, the macro calculator builds directly on that same TDEE estimate.