Your maintenance calories are the amount of energy you'd have to eat, on average, to keep your weight stable — not gaining, not losing. Every diet target is derived from this number, which is unfortunate, because it isn't a constant. It moves as you lose weight, as your activity changes, and as your body adapts to being in a deficit. Treating a figure you calculated three months ago as still true is one of the most common reasons progress quietly stops.
What the number is made of
Maintenance — total daily energy expenditure, or TDEE — is the sum of four things:
- Resting metabolic rate (RMR): roughly 60–70%. What it costs to stay alive: organs, brain, cell maintenance, breathing. Mostly driven by how much fat-free mass you carry.
- The thermic effect of food: about 10%. Digesting and processing what you eat. Protein costs the most to process, carbohydrate and fat less.
- Exercise activity: highly variable, often 5–15%. Deliberate training. Usually a smaller share than people expect.
- Non-exercise activity thermogenesis (NEAT): 10–30%, and wildly individual. Walking, standing, fidgeting, gesturing, general restlessness. In an overfeeding study, differences in NEAT explained a tenfold difference in how much fat people stored from identical excess calories (Levine et al., 1999).
That last component is why two people of identical size and workout routine can have maintenance levels hundreds of calories apart — and why maintenance is best measured rather than looked up.
How to estimate it (and how wrong the estimate will be)
The standard starting point is the Mifflin-St Jeor equation, which predicts RMR from weight, height, age, and sex:
- Men: RMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5
- Women: RMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) − 161
Then multiply by an activity factor — roughly 1.2 for sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active — to get maintenance.
That's a reasonable first guess and a poor final answer. Prediction equations land within about 10% of measured RMR for most people, which sounds fine until you convert it: 10% of a 2,400 kcal maintenance is ±240 kcal/day — larger than the deficit many people are trying to run. The activity multiplier adds more error still, since it's a coarse label standing in for the highly individual NEAT component above.
Use the equation to get in the neighbourhood. Don't use it to explain why the scale isn't moving.
Why maintenance drifts downward while you diet
Four effects stack, and they all point the same way:
1. You're a smaller body. Less mass costs less to maintain and less to move. Lose 10 kg and your RMR falls simply because there's less of you.
2. Adaptive thermogenesis. Beyond what the size change accounts for, dieting lowers expenditure by roughly a further 10–15% (Rosenbaum & Leibel, 2010). This is the part that feels unfair: two people at the same weight can have meaningfully different maintenance levels if one of them arrived there by dieting.
3. NEAT quietly falls. In a deficit, spontaneous movement decreases — you sit a little more, gesture a little less, take the lift without deciding to. It's not laziness and it isn't visible in a step count, but it can account for hundreds of calories.
4. Exercise gets cheaper. Both because you're lighter and because you get more efficient at the movements you repeat.
Together these mean maintenance is a moving target through the whole of a diet — and a big part of why weight loss stalls at a fixed calorie intake.
What doesn't cause the drift
Age, mostly. The largest analysis of energy expenditure across the lifespan found that, once you adjust for fat-free mass, total expenditure is essentially stable from age 20 to 60, only declining after that (Pontzer et al., 2021). Metabolism doesn't "collapse at 40." What typically changes across those decades is body composition and activity — less muscle, more sitting — which is a different problem with a different solution.
Your metabolism being "damaged." Adaptation is real and measurable, but for ordinary deficits it's in the low hundreds of calories, and it partially reverses when you eat at maintenance again. The dramatic figures that circulate online come from extreme cases — competitive weight-loss interventions with 50+ kg lost — and are contested even there.
The better approach: measure your own
You don't have to predict maintenance. You already generate the data needed to observe it.
If your weight trend has been genuinely flat for three to four weeks, whatever you've been eating on average is your maintenance, with more accuracy than any equation. And if your trend is moving, the rate it's moving tells you how far from maintenance you are: since a kilogram of body fat stores roughly 7,700 kcal, a steady loss of 0.5 kg per week corresponds to something in the region of a 550 kcal/day deficit. (Only "in the region of" — early weight change includes water and glycogen, which is why this reasoning needs a multi-week trend rather than a week, and why the 3,500-calorie rule misleads when applied day to day.)
This is exactly the calculation TrendBody runs continuously: it estimates your trend from noisy daily weigh-ins, then converts the trend's velocity into an implied daily surplus or deficit using Hall's peer-reviewed energy-balance model — which accounts for adaptation instead of assuming a fixed constant. No food logging required, because the scale already integrates everything you ate and everything you burned. The science page explains the model; the engineering write-up has the equations.
Practical rules of thumb
- Recalculate every 5 kg (10 lb) lost, or whenever a plateau outlasts four weeks.
- Prefer measured over predicted. A four-week flat trend beats any calculator.
- Protect fat-free mass with adequate protein and resistance training — it's the main lever you control on the RMR side.
- Watch NEAT, not just workouts. A daily walk defends maintenance more reliably than an extra gym session you're too depleted to complete.
- Expect to spend time at maintenance. Periods of eating at maintenance let adaptation partially recover, and are a normal part of a long diet rather than a failure of one.
This article is general educational information, not medical or nutritional advice. Individual energy needs vary with health conditions and medications; talk to a qualified healthcare professional or registered dietitian for a plan tailored to you.
Sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
- Levine JA, Eberhardt NL, Jensen MD. Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science, 1999. DOI
- Rosenbaum M, Leibel RL. Adaptive thermogenesis in humans. International Journal of Obesity, 2010. PubMed
- Pontzer H, et al. Daily energy expenditure through the human life course. Science, 2021. DOI
- Hall KD, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011. PubMed
