What is TDEE and how is it calculated?

Your body burns energy all day, even when you are doing nothing. Breathing, keeping your heart beating, maintaining body temperature and repairing cells all cost calories. That background cost is called your basal metabolic rate, or BMR. It is the largest single part of most people's daily energy use, often around two thirds of the total, though the exact share depends on how active you are.

TDEE — total daily energy expenditure — adds everything else on top of BMR. It includes the energy of moving around, exercising, digesting food and even fidgeting. If BMR is what you burn lying still, TDEE is what you burn living a normal day. That is why TDEE, not BMR, is the number people use when they plan how much to eat.

The most widely used way to estimate BMR is the Mifflin-St Jeor equation. For men it is 10 × weight in kilograms, plus 6.25 × height in centimetres, minus 5 × age in years, plus 5. For women the same formula ends with minus 161 instead of plus 5. The difference reflects average differences in body composition, and it is one reason the result is an estimate rather than a measurement. Two people with the same age, height and weight can still have different BMRs, because muscle burns more energy at rest than fat does, and the formula does not know your body composition.

Once you have BMR, you multiply it by an activity factor. The standard factors are 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active, 1.725 for very active and 1.9 for extra active. Choosing honestly matters more than choosing hopefully. A desk job with a gym session three times a week is moderately active, not very active, and overestimating activity is the most common reason a TDEE estimate feels too high.

Here is the worked example used on the calculator page. A 30-year-old man, 80 kilograms, 180 centimetres, moderately active: BMR = 10×80 + 6.25×180 − 5×30 + 5 = 1,780 calories per day. Multiply by 1.55 and TDEE = 2,759 calories per day. That does not mean he must eat exactly 2,759 calories. It means that, on average, eating around that amount should roughly maintain his weight, eating less should slowly reduce it, and eating more should slowly increase it.

There are limits worth stating plainly. The formula was developed from population averages, so it is less accurate at the extremes — for very muscular people, very small people, older adults and anyone with a medical condition that affects metabolism. It also assumes a stable weight. If you are losing or gaining weight quickly, your actual expenditure is already changing, because a smaller body burns less. Treat TDEE as a starting point, watch what actually happens over two to four weeks, and adjust from there. If you have a health condition, or you are planning a large change in how you eat, talk to a doctor or dietitian first. A free calculator is a good place to start learning, not a substitute for professional advice.

Try it yourself: open the TDEE calculator, enter your own numbers, and then read how to use your TDEE for weight loss, maintenance, or gain.