How to Calculate Your TDEE, Step by Step

Mifflin-St Jeor, times an activity factor, then three weeks of your own data#

Here is how to calculate TDEE in the time it takes to read this paragraph. Estimate your resting metabolic rate with the Mifflin-St Jeor equation, multiply it by an activity factor between 1.0 and about 2.0, and you have a number. That is the whole TDEE calculation formula, and every calculator on the internet is doing exactly this behind a nicer interface.

The part they skip is step three, which is the only one that makes the number yours: track intake consistently for two to three weeks, watch your weight trend, and adjust. The math gets you a bearing. Your own data gets you a position. How far apart those two sit is the reason step three exists — even the best-performing prediction equation in athletes landed within 10 percent of measured resting metabolism in only 80.2 percent of people³, meaning one in five was further out than that before any activity multiplier was applied. TDEE explained makes the case for why the output has to be a range; this article is how you produce the number, and then how you correct it.

Step 1: estimate resting metabolic rate#

Mifflin-St Jeor is the default for good reason. It was built from indirect calorimetry on 498 healthy adults aged 19 to 78 — 264 normal-weight, 234 with obesity — and explains 71 percent of the variance in measured resting energy expenditure¹. In the systematic review that put the major equations head to head, it came out on top: most reliable, predicting resting metabolic rate within 10 percent of measured in more nonobese and obese individuals than any rival, with the narrowest error range².

The equation, in its published form (weight in kg, height in cm, age in years):

RMR = (9.99 × weight) + (6.25 × height) − (4.92 × age) + (166 × sex) − 161

where sex is 1 for men and 0 for women. So for a 34-year-old woman, 68 kg, 168 cm:

(9.99 × 68) + (6.25 × 168) − (4.92 × 34) + 0 − 161 = 679 + 1,050 − 167 − 161 = 1,401 kcal/day

That is the floor: what she'd burn lying still all day. Now it needs an activity factor.

Step 2: apply an activity multiplier#

Physical activity level (PAL) is simply total daily expenditure divided by basal expenditure — a ratio describing how much your day multiplies your resting cost. The Institute of Medicine sorts adults into four bands, and these are the numbers underneath the dropdown on every TDEE calculator⁴:

Category	PAL range	What it looks like
Sedentary	1.0 – 1.4	Desk job, little deliberate movement
Low active	1.4 – 1.6	Desk job plus a walk or a light session most days
Active	1.6 – 1.9	On your feet a lot, or training most days
Very active	1.9 – 2.5	Physical job, or hard daily training

Our 1,401 kcal example, at low active (say 1.5), lands at roughly 2,100 kcal/day. At sedentary (1.3) it's 1,821; at active (1.75) it's 2,452. Notice the span across two adjacent, easily-confused categories: 300-plus calories, for the same woman, on the same day. Your multiplier is a bigger source of error than your equation, and unlike your equation, nobody validated it against anything. You picked it.

Most people overrate themselves here. Three gym sessions a week does not make you "active"; it makes a sedentary person slightly less sedentary. The category is about your whole day, not your best hour of it. When in doubt, choose the lower band — you can always revise upward when your data says so. Activity multipliers explained goes deeper.

The mistake almost everyone makes: adding TEF twice#

Your body spends energy processing meals — breaking food apart, hauling it across the gut wall, putting it away. That is the thermic effect of food, and for a mixed diet at energy balance it lands somewhere between 5 and 15 percent of the day's total⁵. It is a real component, and plenty of guides tell you to add roughly 10 percent for it at the end.

Don't. Total daily expenditure is basal metabolic rate plus the thermic effect of food plus the cost of activity. PAL is defined as total expenditure divided by basal — so when you multiply RMR by a PAL factor, the thermic effect of food is already inside the multiplier. Add another 10 percent on top and you have double-counted it: on a 2,000-calorie target that's a 200-calorie inflation, which is a large fraction of a typical deficit and points in exactly the wrong direction.

Multiply your RMR by an activity factor and you're done. TEF is already in there. Adding it again is a 200-calorie error you'll spend weeks blaming on your metabolism.

The only time you add components separately is if you're building total expenditure from the bottom up — basal, plus TEF, plus activity — rather than using a multiplier. Pick one method and stay in it.

Which equation should you actually use?#

"Best equation" depends on who you are, and the answer is less flattering to Mifflin than its reputation suggests.

Equation	Built from	Best for	The limitation
Mifflin-St Jeor	498 adults, indirect calorimetry	General adult population	Significantly underestimates RMR in athletes³
Harris-Benedict	Early 20th-century data	Little reason to prefer it generally	Beaten by Mifflin in the general-adult review; performed acceptably in athletes
Cunningham / Katch-McArdle	Lean body mass	Lean, trained people	Needs a body-fat measurement — itself an estimate with its own error
Ten-Haaf	Athletes	Trained populations	Best in class, and still only 80.2% within ±10%

That athlete meta-analysis is worth dwelling on: 29 studies, 1,430 participants, 100 different equations tested. Only five showed no significant difference from measured values, Mifflin-St Jeor significantly underestimated, and the winner — Ten-Haaf — hit within ±10 percent in 80.2 percent of people while the rest managed 40.7 to 63.7 percent³. Read those last numbers again. For most equations, closer to half the people tested were outside a ±10 percent band.

The general-adult review adds its own caveat, and it is the one that should change how you read every number above: older adults and US ethnic minorities were underrepresented both in developing these equations and in validating them². If you're outside the populations these formulas were built on, your error bars are wider than the published ones and nobody knows by how much. Mifflin vs Harris-Benedict covers the head-to-head.

Practically: use Mifflin-St Jeor unless you're lean and trained, in which case a lean-mass equation is a reasonable alternative — provided your body-fat number came from something better than a guess.

Step 3: the step that actually makes the number yours#

The only accurate way to measure free-living energy expenditure is doubly labeled water, where you drink water enriched with heavy hydrogen and heavy oxygen and researchers track how fast each isotope washes out. It's the gold standard for human energy requirements in daily life⁶ — and it's a lab procedure with isotope costs, not something your phone does.

So you approximate it the slow way, with your own body as the instrument:

Take your calculated TDEE as a starting target. Not a truth. A hypothesis.
Eat at roughly that number for 14-21 days, logging the same way every day. Consistency beats precision here — a steady 15 percent undercount still tracks change faithfully, because the offset gets absorbed into your maintenance estimate. This is the same reason calorie counts are ranges rather than facts.
Weigh yourself under the same conditions and use the weekly average, not single days. Day-to-day scale noise from water and gut contents will swamp a real trend over any shorter window.
Adjust. Weight stable across three weeks? That intake is your maintenance, whatever the calculator said. Drifting down when you meant to maintain? Your real TDEE is higher than estimated. Add or subtract about 100-150 kcal/day and run another two weeks.

After one cycle you have something no equation can give you: a maintenance figure derived from your actual body, your actual job, your actual fidgeting. That's the whole point of finding your maintenance calories, and it's the number you should set a deficit from — not the calculator's.

One last thing worth owning. Your logging is an estimate too, so this loop is calibrating one fuzzy number against another. That's fine, and it's why consistency matters more than accuracy: as long as you log the same way each day, the errors mostly cancel out of the comparison, which is the thing you're actually steering by. How to count calories covers doing it repeatably.

FAQ#

What is the TDEE calculation formula?#

Resting metabolic rate multiplied by an activity factor. Mifflin-St Jeor gives the RMR: (9.99 × weight in kg) + (6.25 × height in cm) − (4.92 × age) + (166 × sex, where male = 1) − 161. Multiply that by a physical activity level between 1.0 (sedentary) and 2.5 (very active). Don't add anything for the thermic effect of food — the multiplier already contains it.

Do I add exercise calories on top of my calculated TDEE?#

No, for the same reason you don't add the thermic effect of food. Your activity multiplier is defined as total expenditure divided by basal, so whatever training you had in mind when you picked "active" is already inside the number. Adding a treadmill readout on top counts the same workout twice, using a number nobody measured. Pick the band that describes your whole week and leave it there.

Should I recalculate my TDEE as I lose weight?#

Yes — but recalculate from your data, not just from the formula. Your weight changes, so the equation's output drops mechanically, and expenditure can also run below what body composition predicts after sustained weight loss. Re-running the two-to-three-week tracking cycle every 4-5 kg is more informative than re-typing your new weight into a calculator.

Sources#

This article was researched and drafted with AI assistance and reviewed for accuracy by the BurnWeek team. It is general information, not medical advice. How we research and correct our articles →