TDEE: how the calculator works out daily expenditure and how to check your number
TDEE (total daily energy expenditure) is everything the body burns in a day: basal metabolism, digesting food and all movement. The FoodGPT calculator multiplies basal metabolism from the Mifflin–St Jeor equation by an activity factor from 1.2 to 1.9, and most of the uncertainty sits in that multiplier. The number is worth testing on yourself against your average weight over two to three weeks.
What TDEE is made of
Expenditure splits into three parts. The US National Academies give these figures in their 2023 energy requirements report: resting expenditure typically accounts for 60 to 70% of the daily total, about 10% goes on digesting food, and physical activity ranges from 15% in sedentary people to 50% in physically active ones. Energy chapter of Dietary Reference Intakes for Energy, 2023.
That shows where the uncertainty lives. The largest part, basal metabolism, is predicted by an equation from height, weight, age and sex. The most variable part, activity, can differ by hundreds of kilocalories between two people with the same job and the same workouts. For how that looks in daily life, see the articles on everyday activities and on calories burned in a workout.
How the calculator gets TDEE
In two steps. First, basal metabolism from the Mifflin–St Jeor equation (the equation and the sample it was derived from are covered in the article on the calorie calculator). Then multiplication by a factor from five steps:
| Factor | Fits | Share of basal metabolism in TDEE |
|---|---|---|
| 1.2 | desk job, no exercise | 83% |
| 1.375 | 1–3 workouts a week | 73% |
| 1.55 | 3–5 workouts | 65% |
| 1.725 | 6–7 workouts | 58% |
| 1.9 | physical job or two workouts a day | 53% |
The last column is arithmetic: if TDEE is basal metabolism times a factor, the share of basal metabolism is one divided by the factor. It shows what each step builds in. The 60–70% range named by the National Academies corresponds to factors of roughly 1.4 to 1.7.
At the 1.2 step, 17% of expenditure is left for everything except rest. If about 10% goes on digesting food, less than 7% remains for a day's movement. For an ordinary day at a desk that is little, and the 1.2 step tends to underestimate expenditure. The FAO/WHO/UNU scale for populations starts higher: a physical activity level of 1.40–1.69 for a sedentary or light lifestyle, 1.70–1.99 for an active one, 2.00–2.40 for a vigorous one, and values above 2.40, the report says, are difficult to maintain for long. FAO/WHO/UNU report on human energy requirements, 2004. The calculator's top step, 1.9, sits inside the active range; it has no steps for 2.0 and above.
In the calorie calculator the same number is called maintenance: it is one calculation, and the second tool adds ranges for losing and gaining weight on top of it.
How to pick a step
Pick by an ordinary week, not your best one: by how much you walk and stand on average, not by how much you would like to. Workouts are only part of activity: steps and housework count too. The steps are defined by workouts per week, so long walks and a job on your feet fit them badly. For how many steps are worth counting, see the article on steps per day.
What a mistake costs depends on basal metabolism. At 1450 kcal neighbouring steps differ by about 250 kcal and the extreme ones (1.2 and 1.9) by a thousand. If you are torn between two steps, pick either: checking against your weight will show the correction anyway.
A fitness tracker gives a different estimate of expenditure with its own error. On how accurate trackers are, see the article on trackers and calories.
How accurate TDEE is
The error has two parts: the basal metabolism equation and the activity step. There is data on the first. In a 2016 check on 30 adults the limits of agreement between basal metabolism equations and measurement ran from 314 to 445 kcal a day. Flack et al., J Acad Nutr Diet, 2016. At a factor of 1.375 an error of 380 kcal in basal metabolism becomes about 520 kcal a day.
For TDEE as a whole the reference method is doubly labeled water, which measures expenditure in everyday life rather than in a lab. A 2024 study of 56 healthy adults aged 20 to 58 compared expenditure measured that way with the predictions of ten equations. None was accurate for individuals: every one had a root-mean-square error above 10%, and even for the best equation only about 43% of participants fell within ±10% of the measured value. The equations generally underestimated expenditure. Prado-Nóvoa et al., Scientific Reports, 2024. The "Mifflin–St Jeor times a factor" scheme the calculator uses was not tested in that study, and its figures cannot be transferred to it exactly. They do show the order of magnitude: for people with different activity levels, estimates from equations differ from measured expenditure by hundreds of kilocalories.
The practical conclusion is one: the TDEE from the calculator is a starting point for observing yourself.
How to check your number
- Work out TDEE and eat at roughly that intake for two to three weeks, without changing habits or daily routine.
- Weigh yourself under the same conditions and look at the weekly average rather than a single day: weight swings within a day, as explained in why weight changes by a kilogram in a day.
- If the average holds, that is your TDEE, and it is more reliable than the formula. If it moves one way, your expenditure differs from the calculated one: adjust the number by a small step and check again.
- Recalculate after a noticeable change in weight or lifestyle: TDEE changes with them.
The check has its own error: it is only as good as your knowledge of what you ate. Typical tracking errors are covered in the article on why the tracker shows a deficit but weight stays the same. How much energy a change in weight costs, and why "deficit times days" arithmetic works worse than it seems, is explained in the articles on calories in a kilogram of fat and on calorie deficit. Expenditure also changes during weight loss: see metabolic adaptation.
When not to trust the calculation, and when to see a doctor
- Pregnancy and breastfeeding: the calculator does not apply to them.
- Under 18: the calculator does not accept that age.
- Medical conditions and regular medication: in these cases a doctor sets calorie intake. On the thyroid and weight, see this article.
- Anxiety around numbers, guilt or fear of food: when calorie counting becomes a problem.
- Weight that goes down without any change in food or activity. The NHS advises seeing a GP if you keep losing weight without changing your diet or exercise routine. NHS page.
You can work out your own TDEE in the TDEE calculator.
Frequently asked questions
- What is TDEE?
- Total daily energy expenditure: basal metabolism, digesting food and physical activity. It is the intake at which weight stays the same on average.
- How does the FoodGPT calculator work out TDEE?
- First basal metabolism from the Mifflin–St Jeor equation (10 × weight + 6.25 × height − 5 × age, plus 5 for men and minus 161 for women), then multiplication by an activity factor from 1.2 to 1.9.
- What share of TDEE is basal metabolism?
- According to the US National Academies, resting expenditure is typically 60–70% of the daily total, about 10% goes on digesting food, and activity accounts for 15 to 50%.
- How accurate is the TDEE from a calculator?
- For an individual the gap can be several hundred kilocalories. In a doubly labeled water comparison (56 adults), the root-mean-square error of each of ten other equations was above 10%.
- How do I check my TDEE?
- Eat at the calculated intake for two to three weeks and follow your average weight week by week. If it holds, the number is right; if it moves, adjust it by a small step and check again.
Read next
- The FoodGPT calorie calculator: how it works and where it goes wrong — The calorie calculator works out basal metabolism with the Mifflin–St Jeor equation, multiplies it by an activity factor from 1.
- Daily calorie intake — There is no universal norm: it depends on weight, height, age, sex, and activity level.
- How many calories are burned by cleaning, walking the dog, and other daily activities — Energy expenditure for household chores is calculated using a single formula and a standard reference: the Compendium of Physical Activities, where each activity is assigned a MET value.
- How many calories are burned during a workout: running, cycling, swimming, gym — An hour of running at a moderate pace for a 70 kg person is about 550–700 kcal, cycling at a leisurely pace is 350–450, swimming is 400–600, and strength training is 200–350.
This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.
Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.