The four things TDEE is made of
Total daily energy expenditure is the sum of four components, and knowing their relative sizes tells you which ones are worth trying to change.
Basal metabolic rate is the largest by far — typically 60 to 70 percent of the total for a moderately active adult. It is the cost of keeping organs running, and it is driven mostly by how much lean tissue you carry.
The thermic effect of food is the energy spent digesting, absorbing and storing what you eat. It runs around 10 percent of intake for a mixed diet, higher for protein and lower for fat and refined carbohydrate. Because it scales with intake, it falls when you diet — one of several reasons a deficit shrinks itself.
Exercise activity thermogenesis is deliberate training. For most people it is smaller than they expect: three gym sessions a week at 400 kcal each is 1,200 kcal, which spread over seven days is about 170 kcal a day.
Non-exercise activity thermogenesis (NEAT) is everything else you do while upright — walking, standing, housework, fidgeting. It is the most variable component between individuals, and it is the one that quietly falls when you are in a deficit, which is why people plateau while eating the same amount.
This calculator prints the resting and digestion components explicitly and lumps the last two together as activity and NEAT, because no formula can separate them from the inputs you can supply at home.
Why the activity multiplier is the weak link
The basal estimate is a regression with published error bounds. The multiplier is a five-way bracket described in words, and it does more damage to the final number than anything else on the page.
Look at the size of the steps. For a 1,762 kcal basal rate, sedentary gives 2,115 kcal and moderately active gives 2,732 — a 617 kcal gap between two adjacent-but-one descriptions that many people would not confidently choose between. Going one bracket too high builds a permanent 250 to 350 kcal error into every target you derive from it.
The brackets also mean different things depending on your job. A nurse on her feet for a twelve-hour shift who never trains may genuinely sit at 1.55, while an office worker who lifts four times a week but otherwise sits still may be closer to 1.375 despite doing more "exercise". The multiplier is about the whole week, not about how many gym sessions you booked.
The practical rule is to choose one bracket lower than the description you would instinctively pick, then correct upwards from evidence. Eat at the estimate for three weeks, track weight as a rolling average, and adjust: if you are gaining 0.25 kg a week, your real TDEE is about 275 kcal below the estimate. Three weeks of your own data beats every refinement of the equation.
Worked example: a 35-year-old man, 178 cm, 82 kg, training four days a week
- Basal rate. Mifflin-St Jeor: 10 × 82 + 6.25 × 178 − 5 × 35 + 5 = 820 + 1,112.5 − 175 + 5 = 1,762.5 kcal/day.
- Activity factor. Four sessions a week with a desk job is the moderately active bracket, 1.55.
- TDEE. 1,762.5 × 1.55 = 2,732 kcal/day.
- Digestion. 10% of 2,732 = 273 kcal.
- Activity and NEAT. 2,732 − 1,762.5 − 273 = 696 kcal — the whole of his training and daily movement.
- Targets. A 20% cut is 2,732 × 0.8 = 2,186 kcal; a 10% lean bulk is 2,732 × 1.1 = 3,005 kcal.
The component breakdown is worth pausing on. His resting metabolism is 1,762 of 2,732 kcal, or 64.5% of the total, while everything he does all day — including four gym sessions a week — accounts for 696 kcal, or 25.5%. This is why adding a fifth session moves the total much less than most people expect, and why protecting lean mass during a deficit matters: the resting component is the one that is large enough for changes in it to be felt.
Compare the same man on the Katch-McArdle route. At 18% body fat his lean mass is 82 × 0.82 = 67.24 kg, so BMR = 370 + 21.6 × 67.24 = 1,822 kcal and TDEE becomes 1,822.4 × 1.55 = 2,824.7 kcal — 2,824.7 − 2,731.9 = 92.8 kcal above the Mifflin figure. That gap is the value of knowing your body composition, and you can estimate it with the Navy body fat calculator.
Turning TDEE into a target
Maintenance is the anchor; everything else is a percentage of it. For fat loss, a deficit of 15 to 25 percent of TDEE suits most people — large enough to produce visible progress in a month, small enough to preserve training quality and adherence. This calculator prints the 20% figure as the cutting target. For muscle gain, a surplus of about 10 percent is the usual recommendation, because the rate at which you can add muscle is limited and a bigger surplus mostly adds fat.
Convert the percentage into a rate before you commit to it. A 20% deficit on 2,732 kcal is 546 kcal a day, which is 3,824 kcal a week, or about 0.50 kg — right in the middle of the usual guidance of 0.5 to 1 percent of body weight per week. The calorie deficit calculator does that conversion and checks it against minimum intake floors.
Then check the floor. A 20% cut is fine at 2,700 kcal maintenance and problematic at 1,500, where it lands at 1,200. If the percentage takes you below roughly 1,500 kcal for men or 1,200 for women, the answer is a smaller percentage held for longer, or more activity, not a lower plate.
Finally, remember that TDEE is not a constant. It falls as you lose weight — both because there is less of you and because NEAT declines — so a target set in January is wrong by March. Recalculate every 4 to 5 kg.
TDEE at each activity level for two basal rates
| Level | Description | Multiplier | BMR 1,500 | BMR 1,800 |
|---|---|---|---|---|
| Sedentary | Desk job, no deliberate exercise | 1.20 | 1,800 | 2,160 |
| Lightly active | Exercise 1–3 days a week | 1.375 | 2,063 | 2,475 |
| Moderately active | Exercise 3–5 days a week | 1.55 | 2,325 | 2,790 |
| Very active | Hard exercise 6–7 days a week | 1.725 | 2,588 | 3,105 |
| Extra active | Physical job or twice-daily training | 1.90 | 2,850 | 3,420 |
At a 1,500 kcal basal rate the gap between sedentary and extra active is 1,050 kcal a day. Choosing the bracket carefully is worth more than choosing the equation carefully.
Assumptions this estimate makes
- The multiplier is a bracket, not a measurement. It is the single largest source of error in the result, and it absorbs several very different components into one number.
- The thermic effect is taken as 10% of intake. A high-protein diet runs above that and a high-fat diet below it, so the digestion slice is an approximation. It also shrinks when you eat less.
- Exercise is inside the multiplier, not added on top. If you also subtract logged workout calories from a tracker, you are counting training twice. That is the most common way a daily budget drifts upward.
- NEAT is assumed stable. It is not: spontaneous movement falls measurably during energy restriction, which is a large part of why deficits under-deliver over months.
- Body composition is invisible to Mifflin-St Jeor. Two 82 kg bodies at 12% and 30% fat get the same answer. Use Katch-McArdle if you know your body fat.
- Adaptive changes are not modelled. Sustained restriction lowers expenditure by more than weight loss alone predicts, and no static equation captures it.
Do not add workout calories to your TDEE
The activity multiplier already includes your training. If you set a target from TDEE and then also eat back the calories a watch says you burned, you have counted the same session twice — often 300 to 500 kcal a day. Either use the multiplier and ignore the watch, or use a sedentary multiplier and add net exercise calories from the calories burned calculator. Never both.
How this compares with measured expenditure
The reference method for total energy expenditure in free-living people is doubly labelled water: you drink water enriched with stable isotopes of hydrogen and oxygen, and the differential rate at which the two disappear from your urine over a fortnight gives carbon dioxide production, and from that, energy expenditure. It is accurate, expensive and used in research rather than in gyms.
What that research shows is that factor-based estimates are unbiased on average and imprecise for individuals. The prediction is right for the group and can be a few hundred calories out for any one person, which is exactly why the advice here is to treat the output as a hypothesis to be tested against three weeks of weight data.
Two neighbouring tools are worth knowing about. The BMR calculator gives you just the basal component with the Mifflin-St Jeor and Harris-Benedict equations side by side. And if you want to see how a given expenditure translates into a goal date, the weight loss timeline calculator re-runs the whole calculation week by week as your weight falls, which is the only honest way to project more than a month ahead.
Once you have a calorie target, the next decision is its composition. Protein is the macro with the strongest evidence for preserving lean mass during a deficit — start with the protein intake calculator, then split the remainder with the macro split calculator.