TDEE Calculator

How TDEE is calculated

Total daily energy expenditure is everything you burn in twenty-four hours. It is built in two steps. First comes basal metabolic rate, the energy your body spends staying alive at complete rest: heart, brain, kidneys, liver, the constant work of maintaining temperature and repairing tissue. For most people that accounts for 60 to 70 per cent of the daily total. Then a multiplier scales it up to cover everything else: digestion, walking around, fidgeting, work, and deliberate exercise.

Basal rate cannot be predicted exactly without a metabolic cart and a ventilated hood, so published equations estimate it from the variables that track it most closely: weight, height, age and sex. Three equations dominate practice, and this calculator runs all three so you can see how much they disagree.

Mifflin-St Jeor

Derived in 1990 from 498 healthy adults, this is the equation most dietitians now default to. When researchers have tested predictive equations against measured resting expenditure, Mifflin-St Jeor has come within 10 per cent of the measured value more often than any of the older alternatives.

Harris-Benedict (1984 revision)

The original Harris-Benedict equation dates from 1919 and overestimates basal rate by roughly 5 per cent for most modern populations, largely because body composition has shifted since the data was collected. The version below is the Roza and Shizgal revision, which is the one worth using if you use Harris-Benedict at all.

Katch-McArdle

The other two equations infer body composition from weight and height. Katch-McArdle skips the inference and works directly from lean body mass, which is where nearly all resting energy expenditure actually happens. Fat tissue is close to metabolically inert by comparison. That makes it the most accurate of the three, but only if your body fat figure is any good. A DEXA scan or a careful set of tape measurements is worth having here; a guess makes the equation worse than the ones it is meant to improve on.

Whichever equation produces the basal figure, the last step is the same: multiply it by an activity factor. That single multiplication is where the estimate becomes fragile.

Sources: Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals, Am J Clin Nutr 51:241–247 (1990); Roza AM, Shizgal HM. The Harris Benedict equation reevaluated, Am J Clin Nutr 40:168–182 (1984); Katch FI, McArdle WD. Exercise Physiology: Energy, Nutrition and Human Performance, 4th ed. (1996).

Choosing an activity multiplier

The five multipliers below come from the standard Harris-Benedict activity scale and are used, essentially unchanged, by every TDEE calculator on the internet. The descriptions matter more than the numbers, because the descriptions are where people go wrong.

The multiplier is the biggest error in the whole calculation

This is the part most calculators skip past, and it matters more than everything else on the page. The gap between the three BMR equations is typically 50 to 150 kcal, a few per cent. The gap between "lightly active" and "very active" on the same basal rate is around 600 kcal a day. One category of overestimation on the activity scale will wreck your number far more thoroughly than picking the wrong equation ever could.

And overestimation is the norm. When self-reported activity is checked against accelerometers or doubly labelled water (the gold standard for measuring real-world energy expenditure), people consistently report far more activity than they perform. Four gym sessions a week feels like a lot, and it is a meaningful health behaviour, but four hours of training spread across 168 hours does not move the needle as much as the scale's wording implies. If the rest of your week is spent sitting, you are closer to lightly active than moderately active, however committed your training is.

The practical advice is simple and slightly deflating: pick the level below the one that feels right. If you are torn between moderate and very active, choose moderate. If you are torn between light and moderate, choose light. An estimate that runs slightly low produces a mild, sustainable deficit when you diet and only a small surplus when you gain. An estimate that runs high produces a diet that does nothing and a bulk that adds fat you did not want. The asymmetry of those two failures is why erring downward is the right default.

Where TDEE estimates mislead

Predictive equations sit within roughly ±10 per cent of measured expenditure for most people, and that band is wider than it sounds. A calculator that hands you 2,500 kcal is really telling you that your true maintenance intake is probably somewhere between 2,250 and 2,750, a 500 kcal spread, which is the difference between losing half a kilo a week and gaining it. For a minority of people the error is larger still. The equations were built on population averages; you are one person, and individual resting metabolic rate varies by several hundred calories between people matched for age, sex, height and weight.

Three specific things break the estimate more than anything else.

Adaptive thermogenesis

Your TDEE is not a constant. During a prolonged calorie deficit it falls, and it falls by more than the loss of body mass alone would predict. Resting rate drops, spontaneous movement drops, the energy cost of a given amount of work drops slightly. The much-discussed follow-up study of The Biggest Loser contestants found resting metabolic rate suppressed by several hundred calories a day years after the competition ended. Most people dieting sensibly see something far milder, but the direction is consistent: the longer and harder you diet, the further your real TDEE sits below the number this page gave you on day one. Recalculate every few weeks as your weight changes, and expect to need periodic breaks at maintenance.

NEAT varies enormously

Non-exercise activity thermogenesis covers everything you burn that is not sleeping, eating or deliberate exercise: walking to the kitchen, standing on a call, fidgeting, gesturing, maintaining posture. Overfeeding studies have found NEAT differences of up to roughly 2,000 kcal a day between individuals given identical surplus calories. Some people unconsciously move far more, and gain far less. No activity multiplier can capture this, because you do not know where you sit on that distribution and neither does the equation. It is the single largest reason two people of identical size and training habits can have genuinely different maintenance intakes.

Body composition the equation cannot see

Mifflin-St Jeor and Harris-Benedict take weight as a proxy for metabolically active tissue. For a lean, heavily muscled person that proxy undershoots; for someone carrying substantial fat mass it overshoots. This is exactly the case Katch-McArdle was designed for, which is why this calculator offers it as soon as you supply a body fat figure. If you do not have a reliable one, our body fat calculator will get you closer than a guess.

None of this makes the estimate useless. It makes it a starting point rather than an answer. The only way to know your real maintenance intake is to measure it on yourself.

How to calibrate the number against reality

This is the protocol that turns a population estimate into your own figure. It takes two to three weeks and it is more accurate than any equation, because it measures the one system that matters, which is yours.

Step one: log everything for fourteen days. Not approximately, not most things. Weigh food where you can, log restaurant meals as their closest database match, and include the oil in the pan, the milk in the coffee and the beer on Friday. Under-reporting of intake is the best-documented failure in nutrition research. Studies comparing food diaries against doubly labelled water routinely find people eating substantially more than they record, and the effect grows with body weight. Fourteen days is the minimum because it smooths out a weekend, a bad night's sleep and a heavy training block.

Step two: weigh yourself daily and average by week. Same time, same conditions, first thing in the morning after the bathroom and before eating. Individual daily weights are noise: glycogen, sodium, digestive contents and hydration move the scale a kilo or more in either direction for reasons that have nothing to do with body fat. What you want is the average of days 1–7 and the average of days 8–14. The difference between those two averages is your real weekly drift.

Step three: back-calculate. A kilogram of body fat stores roughly 7,700 kcal (about 3,500 kcal per pound). So if your weekly averages fell by 0.4 kg while you ate an average of 2,400 kcal a day, you were running a deficit of about 3,080 kcal across the week, or 440 kcal a day. That puts your true maintenance intake near 2,840 kcal, not whatever the calculator said.

Two cautions on that arithmetic. It assumes the weight you lost was fat, which holds reasonably well over a two-week window in someone whose training and sodium intake are stable, but not in the first week of a new diet when most of the drop is water and glycogen. Start the clock after that initial flush. And it assumes your logging was honest. If the calculated number comes out implausibly low, the likeliest explanation is not a broken metabolism but calories that never made it into the diary.

Once you have your own number, keep using it and keep checking it. Re-run the two-week audit whenever your weight has moved by 5 per cent or your training has changed substantially. Then take the calorie target into our macro calculator to split it into protein, carbohydrate and fat.

Common questions