TDEE, total daily energy expenditure, is the number of calories you burn in a day, so eating that amount keeps weight stable. It combines resting metabolism, digestion (about 10%) and activity. Doubly labelled water studies of 6,421 people show size-adjusted expenditure stays stable from about 20 to 60, so a formula estimate is a starting point you refine with real weight data.
Key takeaways
- TDEE is resting metabolism plus digestion (about 5–15%) plus all activity, including everyday movement called NEAT.
- Calculators use Mifflin-St Jeor times an activity factor; the activity level you choose can shift the result by 300 kcal or more.
- Mifflin-St Jeor is the most reliable common formula but can still be off by 10% or more for an individual.
- Size-adjusted metabolism stays stable from about 20 to 60 and declines about 0.7% a year after that.
- Use your estimate for two to four weeks, then adjust it from your weekly average weight.
What is TDEE, in plain words?
TDEE stands for total daily energy expenditure: the calories your body uses in a full day. Eat about that much and your weight stays roughly stable, which is why it is also called your maintenance number. Eat less and you are in a calorie deficit; eat more and you are in a surplus.
TDEE has three parts:
- Basal or resting metabolism. The energy that keeps you alive at rest: breathing, circulation, brain, organs. For most people this is the largest share.
- Thermic effect of food. The energy used to digest and store what you eat. A classic review found it is about 5–15% of daily expenditure on a mixed diet, roughly 10% on average. It is higher for protein (about 20–30% of protein calories) than for carbohydrate (5–10%) or fat (0–3%).
- Activity. Planned exercise plus everything else you do on your feet: walking, chores, standing, fidgeting. That second part is called NEAT, non-exercise activity thermogenesis.
For example, a 520 kcal chicken and rice plate (Sporty's per-serving estimate; real values depend on recipe and portion) costs roughly 50 kcal to digest at a typical 10%.
How is your maintenance number calculated?
Most calculators, including Sporty's, start with the Mifflin-St Jeor equation for resting energy:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
The result is multiplied by an activity factor: 1.2 (sedentary), 1.375 (lightly active), 1.55 (moderately active), 1.725 (very active) or 1.9 (extremely active).
| Example | Resting energy | × 1.2 | × 1.375 | × 1.55 |
|---|---|---|---|---|
| Woman, 30, 65 kg, 165 cm | ≈ 1,370 kcal | ≈ 1,645 | ≈ 1,885 | ≈ 2,125 |
| Man, 35, 80 kg, 178 cm | ≈ 1,745 kcal | ≈ 2,090 | ≈ 2,395 | ≈ 2,700 |
Notice how much the activity factor moves the result: for the man, going from "lightly" to "moderately active" adds about 300 kcal a day. Try your own numbers here:
Daily calorie calculator
Mifflin-St Jeor equation × activity factor. Capped at the usual minimum (1,200 kcal women / 1,500 kcal men); going lower needs medical supervision. Estimates only.
How accurate is a TDEE estimate?
It is a good starting point, not a measurement. A systematic review of prediction equations found Mifflin-St Jeor was the most reliable of the common formulas, predicting resting energy within 10% of the measured value in more people than any other equation. It also warned that individual errors can still be noteworthy, and that older adults and some ethnic groups were under-represented in the research.
For the man above, a 10% error is about 175 kcal of resting energy a day. Add uncertainty in the activity factor and two people with the same numbers can differ by a few hundred calories. That is why the best "calculator" is your own data: eat a steady amount for two to four weeks and watch your weekly average weight.
Is your maintenance number the same every day?
No. TDEE is better thought of as a weekly average than a fixed daily number. A day with a long walk, a gym session or a house move burns more than a day at the desk, and a bigger meal costs a little more to digest. That is why your weight trend over weeks tells you more than any single day. If your average weight stays flat while you eat a steady amount, that amount is your real maintenance, whatever the calculator said.
What have doubly labelled water studies taught us?
Doubly labelled water is the gold-standard way to measure total energy use in daily life: you drink water tagged with harmless isotopes, and urine samples show how much energy you burned over one to two weeks. Large databases of these measurements have overturned some popular beliefs.
- Metabolism does not slow down in your 30s or 40s. A 2021 study in Science of 6,421 people aged 8 days to 95 years in 29 countries found that, after adjusting for body size and composition, energy expenditure stays stable from about 20 to 60, even during pregnancy. It starts to fall around 60, by about 0.7% a year.
- Your body partly offsets extra activity. A 2021 analysis of 1,754 adults found that, on average, about 28% of the calories burned through extra activity were offset by lower basal energy use. Only about 72% showed up in total daily expenditure.
- Very high activity can plateau. A 2016 study of 332 adults in five countries found that total expenditure rose with activity at lower levels but levelled off at higher levels.
The practical message: middle-age weight gain is more likely about eating and moving habits than a sudden metabolic slowdown, and adding exercise burns somewhat less than a fitness tracker suggests.
Why does NEAT matter so much?
NEAT is the most variable part of TDEE. In a classic 1999 experiment, 16 adults ate 1,000 kcal a day above their needs for eight weeks. About two-thirds of the rise in their energy use came from NEAT, and differences in NEAT explained a tenfold difference in how much fat people stored.
You cannot easily control fidgeting, but you can control walking. More steps raise NEAT; see how many steps a day help with weight loss.
How do you use your TDEE to lose weight?
- Pick the honest activity level. If you sit most of the day and train three times a week, "lightly active" is usually closer than "moderately active".
- Subtract a modest deficit. About 500 kcal a day leads to roughly 0.5 kg a week at first. See how many calories to eat to lose weight.
- Do not count exercise twice. Your activity factor already includes it, so do not also add back tracker calories.
- Keep protein up. It has the highest thermic effect and helps keep you full; see how much protein per day.
- Recalculate after every 4–5 kg. A smaller body needs less energy, so your maintenance number drops as you lose weight. When progress stalls, read what a weight loss plateau is.
Do not go below about 1,200 kcal (women) or 1,500 kcal (men) a day without medical supervision. If you are pregnant, under 18, or have a medical condition or a history of disordered eating, talk to a doctor or registered dietitian before setting a target.
Frequently asked questions
Is TDEE the same as BMR?
No. BMR, or resting energy, is only what you burn at rest. TDEE adds the energy used to digest food and all your activity, so it is always higher.
Does metabolism slow down with age?
A 2021 doubly labelled water study of 6,421 people found size-adjusted energy expenditure is stable from about 20 to 60 and declines about 0.7% a year after 60.
Should I eat back calories from exercise?
If your activity factor already includes your training, no; adding them back counts exercise twice. Adjust based on your weekly average weight instead.
How often should I recalculate my TDEE?
After every 4–5 kg lost or gained, or when your activity changes a lot, because a smaller body needs less energy.
Why is my real maintenance different from the calculator?
Formulas estimate the average person with your size, age and sex. Resting energy can differ by 10% or more between individuals, and activity levels are easy to over- or underestimate.
Sources
- Pontzer et al. 2021, Daily energy expenditure through the human life course (Science)
- Careau et al. 2021, Energy compensation and adiposity in humans (Current Biology)
- Westerterp 2004, Diet induced thermogenesis (Nutrition & Metabolism)
- Frankenfield et al. 2005, Comparison of predictive equations for resting metabolic rate: systematic review
- Levine et al. 1999, Role of nonexercise activity thermogenesis in resistance to fat gain (Science)
This article is general information, not medical advice. If you have a health condition, are pregnant or under 18, talk to a doctor or registered dietitian before changing your diet.