Understanding Your TDEE: Total Daily Energy Expenditure Explained

Total daily energy expenditure (TDEE) is the number of calories you burn in a typical day, and the calculator estimates it as basal metabolic rate (BMR) multiplied by an activity factor from 1.2 to 1.9. For a 34-year-old man who is 175 cm tall, weighs 78 kg and trains three to five days a week, that works out to about 2,649 kcal per day. It is an estimate built from four inputs, not a measurement, and the useful question is which of those inputs can move it most.

The two-step calculation

Step one is BMR, the energy your body uses at complete rest. Our calculator uses the Mifflin-St Jeor equation: 10 x weight in kg + 6.25 x height in cm - 5 x age + 5 for men (minus 161 for women). For this man that is 780 + 1,093.75 - 170 + 5 = 1,709 kcal. Step two multiplies BMR by the activity factor you choose. Everything the body does on top of resting, from walking to the car to a hard workout, is folded into that single number.

Assumptions for every figure in this post: male, 34 years old, 175 cm, 78 kg, no body fat percentage entered, so Mifflin-St Jeor applies. Values are rounded to the nearest kcal. The person is illustrative, not an average.

What moves the estimate, and by how much

Because TDEE is a product of two terms, you can change one input at a time and see its effect. The table starts from the moderate-exercise result and changes a single input.

The pattern is clear. A 5 kg change in weight shifts the result by about 78 kcal, and ten years of age shifts it by about 78 kcal, because Mifflin-St Jeor subtracts 5 kcal of BMR per year, which is 50 kcal per decade, or about 2.9% of this man's BMR. Choosing the wrong activity step moves the answer by about 299 kcal, several times more than any of the body measurements. The input you are most likely to guess wrong is also the one that matters most.

How the calculator splits TDEE into components

The results panel breaks TDEE into BMR, thermic effect of food (TEF), exercise (EAT) and everyday movement (NEAT). Be clear about how: TEF is set to 10% of TDEE, EAT to a fixed share that rises with the activity level (2%, 5%, 10%, 15% and 20% for the five factors), and NEAT is simply what remains. For this man at factor 1.55 that gives BMR 1,709, TEF 265, EAT 265 and NEAT 410 kcal. The breakdown is an allocation model that always adds back to the total. It is a helpful picture of where calories go, not a measurement of your own TEF or NEAT, which differ from person to person.

When you know your body fat percentage

If you enter a body fat percentage the calculator switches to the Katch-McArdle equation, BMR = 370 + 21.6 x lean mass in kg. It ignores age, height and sex and looks only at lean mass. Here is the same man at different body fat levels, still at factor 1.55:

The two equations agree almost exactly at 20% body fat for this man and drift apart on either side, by roughly 223 kcal at 12% and 247 kcal at 30%. A rough guess at body fat can therefore swing the answer by hundreds of kcal, so only enter a figure you trust. Harris-Benedict, which the calculator shows for comparison, gives a BMR of 1,780 kcal and a TDEE of 2,759 kcal for this man, about 111 kcal above Mifflin-St Jeor.

Using the number

• Treat 2,649 kcal as the first guess for maintenance. Eat near it for two to three weeks while weighing yourself the same way each day, then adjust from what the scale average does.
• The calculator's goal rows are simple offsets: 250 or 500 kcal below TDEE for loss and 250 or 500 above for gain, with the rough rule of 500 kcal a day being about 1 lb a week. That rule is an approximation that drifts as your body changes.
• TDEE falls as weight falls. If this man drops 8 kg (78 to 70 kg), Mifflin-St Jeor lowers his BMR by 80 kcal and his TDEE at 1.55 by 124 kcal, so recalculate every few kilograms.

Common mistakes and limits

• Picking the activity factor by ambition. Choose by what an average week actually looks like, and if you are between two levels, start with the lower one.
• Eating at BMR. BMR excludes all movement, so for this man it sits about 940 kcal below his estimated maintenance.
• Treating the components as personal facts. The 10% TEF and fixed EAT shares are model assumptions.
• Ignoring conditions the equations cannot see. Medical conditions, medications, pregnancy and breastfeeding all change energy needs, and none is an input.