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Maintenance calories: a formula, or measured
Your maintenance is how many kilocalories a day keep your weight where it is. A formula can guess it from your height, weight, age and sex. A few weeks of your own diary and scale can measure it.
What are maintenance calories, and what is TDEE?
Maintenance calories and TDEE, total daily energy expenditure, are two names for the same thing: everything your body uses in a day. Most of it goes on keeping you running at rest. The rest goes on digesting food and on moving, from the walk to the shop to a training session.
Eat that much on average and your weight holds. Eat more and, over weeks, it rises; eat less and it falls. Every daily target is set from this one number, so a target is only as right as the maintenance under it.
How does a formula like Mifflin–St Jeor work?
Most calculators start from the Mifflin–St Jeor equation, published in 1990 from measurements of 498 healthy adults aged 19 to 78. It estimates the energy you use at rest:
10 × weight in kg + 6.25 × height in cm − 5 × age in years, then + 5 for men or − 161 for women
For a 35-year-old woman of 1.70 m and 70 kg, that is 700 + 1,062.5 − 175 − 161: about 1,430 kcal a day at rest. A calculator then multiplies this by an activity factor to reach a total for the day.
How far off is the formula for one person?
On average, not far. A systematic review of the common equations found Mifflin–St Jeor the most reliable of them: it came within 10% of measured resting energy for more people than any other. The same review warns of noteworthy errors once it is applied to one person.
In a 2020 study of 125 women whose resting energy was measured in a laboratory, the formula came within 10% for 71% of them. For nearly three in ten, it was further off. For the woman above, 10% is already about 140 kcal a day, before anything is added for activity.
The formula knows only weight, height, age and sex. In Mifflin's own data, fat-free mass, which is everything in the body that is not fat, predicted resting energy better than weight did. Two people of the same weight and height can carry very different amounts of muscle, and the formula cannot tell them apart.
Why is the activity factor a guess?
The resting figure is multiplied by a factor for how active you are. Many calculators offer steps like these, shown here for the woman above:
| Factor | Often described as | Maintenance |
|---|---|---|
| 1.2 | Mostly sitting, little exercise | 1,710 kcal |
| 1.375 | Light exercise, 1 to 3 days a week | 1,960 kcal |
| 1.55 | Moderate exercise, 3 to 5 days a week | 2,210 kcal |
| 1.725 | Hard exercise, 6 or 7 days a week | 2,460 kcal |
One choice in a menu, and the same person comes out anywhere between about 1,700 and 2,450 kcal. The boxes are wide, too. The FAO, WHO and UNU report on human energy requirements gives a sedentary or lightly active lifestyle a factor of 1.40 to 1.69: within that one box, about 410 kcal a day for the woman above. You pick a box; the formula cannot check whether it fits your days.
How can you measure your maintenance instead?
By energy balance. If your weight holds steady while you eat a certain amount on average, that amount is your maintenance. If your weight moves, the change says how far apart what you ate and what you burned were.
The usual conversion is about 7,700 kcal per kilogram of body weight, the metric form of the familiar 3,500 kcal per pound. So:
maintenance ≈ average intake a day − (change in weight in kg × 7,700 ÷ number of days)
A worked example, in round numbers:
| Days logged between two weigh-ins four weeks apart | 28 |
| Average intake a day, from the diary | 2,000 kcal |
| Change in the weight trend, 80.0 to 79.2 kg | −0.8 kg |
| The energy that change stands for, 0.8 × 7,700 | 6,160 kcal |
| Per day, 6,160 ÷ 28 | 220 kcal |
| Maintenance a day, 2,000 + 220 | about 2,220 kcal |
The weight went down, so more was burned than eaten: maintenance is the intake plus the difference.
There is a quiet advantage in measuring this way. Studies of food records find, again and again, that people record less than they eat: a forgotten handful, a generous pour. A formula cannot know about that. A measured maintenance takes it in. If your diary misses 200 kcal a day, the maintenance it measures comes out 200 kcal lower too, and a target set from it fits the diary you actually keep.
How exact is 7,700 kcal per kilogram?
Good enough as a rule of thumb, with three caveats.
- It is an average. A kilogram of body weight is never pure fat; how much energy it holds depends on how much of it is fat, lean tissue and water, and on how much body fat you have to begin with.
- Water moves first. Muscle and liver store carbohydrate as glycogen, about 600 g in all, and each gram is stored with at least 3 g of water. When what you eat changes, that store fills or empties within days, which can move the scale by a kilo or more that holds almost no energy. The first week after a change says little.
- It converts a change you have measured; it is poor at predicting one. Used to forecast weight over months, the rule overstates how much will change, because what you burn changes as your weight does. A measured maintenance is best measured again as time goes on, not set once.
Why does it take at least two weeks?
Because one weigh-in is noisy. A man who weighed himself every morning, under the same conditions, for more than 25 years saw his weight move by a typical 0.5% from one day to the next, about 0.4 kg at 80 kg, without anything real changing.
Over a short period, that noise swamps the answer. Half a kilo of water at either end reads as 3,850 kcal of body tissue. Spread over:
| Period | Result off by |
|---|---|
| 1 week | 550 kcal a day |
| 2 weeks | 275 kcal a day |
| 4 weeks | about 140 kcal a day |
What you eat varies too: a week with a dinner out looks different from the next. Two weeks is the least that evens out a weekend or two, and longer is better. Reading the change from a trend line rather than from two single weigh-ins takes out much of the water as well; the guide to why your weight goes up and down explains how.
How does Unpound measure your maintenance?
When you set Unpound up, it starts from the guess: Mifflin–St Jeor with the activity level you choose. From then on it measures.
- After fourteen logged days and two weigh-ins at least ten days apart, it takes your average intake on the logged days between those weigh-ins and corrects it by how much your weight trend changed, at 7,700 kcal per kilogram. It looks back over the last six weeks.
- Only whole days count: a day you rounded off, or one where you logged at least half your target. A day logged up to breakfast would otherwise pass for a day of eating little. A day with a meal still planned in pencil sits out, since nobody knows yet whether it was eaten.
- The change is read off the trend line, not off two single weigh-ins.
- It never changes your target by itself. Use as daily target applies it with one tap. The figure moves as new days come in, and each week's is kept, so you can see how it changed.
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51(2):241–247. doi:10.1093/ajcn/51.2.241 · PubMed
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005;105(5):775–789. doi:10.1016/j.jada.2005.02.005 · PubMed
- Thom G, Gerasimidis K, Rizou E, et al. Validity of predictive equations to estimate RMR in females with varying BMI. J Nutr Sci 2020;9:e17. doi:10.1017/jns.2020.11 · PubMed
- FAO, WHO, UNU. Human energy requirements: report of a Joint FAO/WHO/UNU Expert Consultation. FAO Food and Nutrition Technical Report Series 1. Rome, 2004. Chapter 5, table 5.3. fao.org
- Hall KD. What is the required energy deficit per unit weight loss? Int J Obes 2008;32(3):573–576. doi:10.1038/sj.ijo.0803720 · PubMed
- Thomas DM, Martin CK, Lettieri S, et al. Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. Int J Obes 2013;37(12):1611–1613. doi:10.1038/ijo.2013.51 · PubMed
- Murray B, Rosenbloom C. Fundamentals of glycogen metabolism for coaches and athletes. Nutr Rev 2018;76(4):243–259. doi:10.1093/nutrit/nuy001 · PubMed
- Schneditz D, Hofmann P, Krenn S, et al. Day-to-day variability in euvolemic body mass. Ren Fail 2023;45(2):2273421. doi:10.1080/0886022X.2023.2273421 · PubMed
- Ravelli MN, Schoeller DA. Traditional self-reported dietary instruments are prone to inaccuracies and new approaches are needed. Front Nutr 2020;7:90. doi:10.3389/fnut.2020.00090 · PubMed
More guides
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Counting calories, and keeping it up
When to log, what to repeat, and what to do about a missed day.
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Why your weight goes up and down from day to day
Water, glycogen, salt and your cycle, and what a trend line shows.
Unpound is a calorie diary for iPhone that does this measuring for you, from the diary you keep.
