What Is TDEE? Total Daily Energy Expenditure Explained

TDEE stands for total daily energy expenditure: all the calories your body uses in 24 hours to stay alive at rest, digest food and move. The FAO puts resting energy at 45 to 70 percent of the total, depending on age and lifestyle. A woman who is 42, 168 cm and 68 kg lands between 2,048 and 2,595 kcal on the 2023 US energy equation, depending on how active she is.

What does TDEE stand for, and what does it mean?

It means the number of calories you burn in a day, all 24 hours of it, sleep included. Eat exactly that much and your weight stays flat. The NHS puts an average woman at 2,000 kcal and an average man at 2,500 kcal. How far your own figure strays from those is the question behind how many calories per day you need.

Research reports use other names for the same idea. The 2023 NASEM report says total energy expenditure, or TEE. It also defines the estimated energy requirement, or EER, and notes that in a weight-stable person, TEE is the most accurate measure of EER. For a weight-stable adult, “maintenance calories”, “TEE” and “EER” end up as one figure. I’ll stick to TDEE.

What is inside your TDEE?

Three parts: resting metabolism, the energy cost of digesting food, and physical activity. NASEM writes that TEE comprises basal or resting metabolic rate, thermic effect of food and physical activity, and the FAO lists the same three.

• Basal metabolic rate (BMR) is the energy for staying alive at rest. The FAO defines it as the minimal rate of energy expenditure compatible with life, measured lying down, fasting and relaxed.
• Thermic effect of food (TEF) is the energy used to digest, absorb and process what you eat. NASEM puts it at approximately 10 percent of TEE. The FAO says about 10 percent of BMR, a smaller figure.
• Physical activity is the most variable part. The FAO splits it into obligatory activity (work, school, housework) and discretionary activity (exercise, leisure).

I built a breakdown for one woman, 42 years old, 168 cm and 68 kg, using NASEM’s four activity categories for the total. For resting energy I used the Mifflin–St Jeor equation, fitted to 498 healthy adults: 10 × 68 + 6.25 × 168 − 5 × 42 − 161 = 1,359 kcal. TEF is 10% of the total, and activity is what’s left. This is my arithmetic, not a measurement.

Activity category	TDEE (kcal)	Resting (kcal, share)	TEF at 10% (kcal)	Activity (kcal, share)
Inactive	2,048	1,359 (66%)	205	484 (24%)
Low active	2,216	1,359 (61%)	222	635 (29%)
Active	2,354	1,359 (58%)	235	760 (32%)
Very active	2,595	1,359 (52%)	260	976 (38%)

All four resting shares, 52 to 66%, sit inside the FAO’s range of 45 to 70%. Resting energy stays put from row to row. Of the 547 kcal between the inactive and the very active woman, 492 land in activity and 55 in extra digestion.

Use the FAO’s version of TEF and 10% of 1,359 is 136 kcal. That frees about 86 kcal for the activity slice of the low active row. Nothing important changes. TEF is small. I wouldn’t lose an evening over it.

Is TDEE the same as BMR or maintenance calories?

Maintenance calories are the TDEE of someone whose weight isn’t changing, so in practice they are the same number. BMR is only one ingredient of it, and BMR vs TDEE covers where the line falls.

The gap between the two has a name. The FAO defines the physical activity level, or PAL, as TEE divided by BMR. A PAL of 1.4 means 1.4 times your resting energy. In the table above the Mifflin figure and the NASEM totals imply PALs of 1.51, 1.63, 1.73 and 1.91. But NASEM’s own typical values are about 1.4, 1.6, 1.75 and 2.05 for the four categories. Part of that mismatch comes from mixing two equations, so keep each calculator’s parts together. Don’t mix.

Calories and kilojoules measure the same thing. Australian labels give kJ, and 1 kcal = 4.184 kJ per the FAO conversion table, so a 2,048 kcal TDEE is 8,569 kJ.

How is TDEE measured, and how do calculators estimate it?

The lab method is doubly labeled water. You drink water tagged with two isotopes. The rate at which each leaves your body shows how much carbon dioxide you produce. That gives your energy use. NASEM calls it the benchmark standard in the nutrition community. A run takes 7 to 14 days.

Calculators skip the lab and predict. NASEM built its equations from a pooled database of 8,600 such measurements across all ages. They need age, height, weight, sex and an activity category. Their root-mean-square error is 246 kcal a day for women and 339 kcal for men, which is the whole story of how accurate TDEE calculators are.

They don’t agree with each other, either. Take the same woman and run the common shortcut: Mifflin resting energy times the sedentary 1.2 factor. It gives 1,631 kcal. NASEM’s inactive row gives 2,048 kcal. That is a 417 kcal gap before anyone has argued about activity.

Enter your age, height, weight and activity in the calorie calculator and it returns your TDEE from the NASEM 2023 equations. Any target it sets stays at or above 1,200 calories for women and 1,500 for men.

Does TDEE change with age and weight?

The NASEM equations treat weight and age as plain coefficients. Each kg adds 11.71 to 12.56 kcal for women and 14.10 to 19.11 kcal for men. Each year of age takes off 7.01 kcal for women and 10.83 kcal for men. For a woman, ten more years cost about 70 kcal and ten more kg add 117 to 126.

A 2021 Science study of doubly labeled water data found that expenditure adjusted for fat-free mass was stable from 20 to 60 and declined in older adults. My reading is that the equation can’t see your fat-free mass, so age stands in for it.

What do I do with my TDEE?

Eat near it and your weight holds; below it you lose, above it you gain. How far you move from it is a separate decision that depends on your health and goals.

NASEM sets out a two-step plan for using its equation: calculate the estimate, then monitor body weight over time and adjust intake in increments. My version of step two: weigh yourself 3 mornings a week for two weeks while you eat close to the estimate. If the weekly averages stay within about 0.5 kg (1 lb) of each other, the estimate is close. If they keep climbing or falling, move your number by 100 to 200 kcal and test again. The 0.5 kg band and the step are my rules. The 246 to 339 kcal error is why I don’t trust any single calculator to the nearest 50.

I recompute my TDEE when my weight changes by 5 kg or more, or when my routine changes for a month. These equations cover adults, so if you’re pregnant or breastfeeding, or have a health condition or take a medicine that changes your weight or appetite, your doctor or midwife sets your energy target.