Every diet ultimately works the same way: it creates a caloric deficit. Whether it is keto, intermittent fasting, paleo, or plain calorie counting, the mechanism is identical. You consume fewer calories than your body burns. The number your body burns is your Total Daily Energy Expenditure, or TDEE.
If you do not know your TDEE, you are guessing. And guessing is why most diets fail.
What TDEE actually is
TDEE is the total number of calories your body burns in a day. It has four components:
Basal Metabolic Rate (BMR): The calories your body burns at complete rest just to keep you alive -- heartbeat, breathing, brain function, cell repair. This is typically 60-75% of TDEE.
Thermic Effect of Food (TEF): The energy required to digest and process food. Roughly 10% of total calorie intake. Protein has a higher thermic effect (~25%) than carbs (~8%) or fat (~3%).
Non-Exercise Activity Thermogenesis (NEAT): Calories burned through daily movement that is not intentional exercise -- walking, fidgeting, standing, typing. This varies enormously between people, from 200 to 900+ calories per day.
Exercise Activity Thermogenesis (EAT): Calories burned during intentional exercise. For most people, this is 5-10% of TDEE unless they are serious athletes.
TDEE = BMR + TEF + NEAT + EAT
Calculating BMR
The two most widely used BMR formulas are:
Mifflin-St Jeor (more accurate for most people):
Men: BMR = 10 * weight(kg) + 6.25 * height(cm) - 5 * age - 161 + 166
Women: BMR = 10 * weight(kg) + 6.25 * height(cm) - 5 * age - 161
Harris-Benedict (original, slightly less accurate):
Men: BMR = 88.362 + 13.397 * weight(kg) + 4.799 * height(cm) - 5.677 * age
Women: BMR = 447.593 + 9.247 * weight(kg) + 3.098 * height(cm) - 4.330 * age
For a 30-year-old male, 180cm, 80kg:
Mifflin-St Jeor: 10(80) + 6.25(180) - 5(30) + 5 = 1,780 calories/day
Harris-Benedict: 88.362 + 13.397(80) + 4.799(180) - 5.677(30) = 1,856 calories/day
These formulas have a margin of error of about 10%. They are estimates, not measurements. The only way to know your exact BMR is indirect calorimetry, which measures oxygen consumption in a clinical setting.
From BMR to TDEE
Multiply BMR by an activity factor:
- Sedentary (desk job, no exercise): BMR * 1.2
- Lightly active (exercise 1-3 days/week): BMR * 1.375
- Moderately active (exercise 3-5 days/week): BMR * 1.55
- Very active (exercise 6-7 days/week): BMR * 1.725
- Extremely active (athlete, physical job + exercise): BMR * 1.9
For our example at moderately active: 1,780 * 1.55 = 2,759 calories/day.
Using TDEE for weight management
To lose weight: Eat 300-500 calories below TDEE. A 500-calorie daily deficit produces roughly 1 pound of weight loss per week (3,500 calories per pound of body fat). Larger deficits are unsustainable and cause muscle loss.
To gain weight: Eat 300-500 calories above TDEE. Combined with resistance training, this supports muscle growth with minimal fat gain.
To maintain: Eat at TDEE. Track your weight over 2-3 weeks. If it is stable, your TDEE estimate is correct. If it drifts, adjust by 100-200 calories.
The precision matters. The difference between a 300-calorie deficit and a 100-calorie surplus is a single snack. Without knowing your TDEE, it is impossible to know which side of the line you are on.
Why adaptive tracking is essential
TDEE is not static. As you lose weight, your BMR decreases (less body mass to maintain). As you gain muscle, your BMR increases. Seasonal activity changes, stress levels, sleep quality, and hormonal fluctuations all affect TDEE.
The practical approach is to recalculate every 2-4 weeks and adjust intake accordingly. Better yet, use your actual weight trend as feedback. If you are in a 500-calorie deficit and not losing weight after 3 weeks, your TDEE estimate was too high. Adjust down by 200 calories and observe again.
I built a TDEE calculator at zovo.one/free-tools/tdee-calculator that computes your BMR using both Mifflin-St Jeor and Harris-Benedict, applies activity multipliers, and gives you calorie targets for loss, maintenance, and gain. It takes 30 seconds and gives you the single number that makes every dietary decision downstream more informed.
I'm Michael Lip. I build free developer tools at zovo.one. 500+ tools, all private, all free.
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