How to Calculate Your TDEE: The Mifflin-St Jeor Method

Almost every calorie goal you have ever seen — “eat 500 below maintenance to lose a pound a week,” “hit a small surplus to build muscle” — is measured relative to one number: your Total Daily Energy Expenditure, or TDEE. It’s the total number of calories your body burns in a day. Get it roughly right and every target that follows is anchored to reality. Get it wrong and you’re guessing. The good news is that a well-validated formula gets you close in about two minutes of arithmetic, and the TDEE & Macro Calculator will run it for you.

This piece walks through how to calculate TDEE by hand so you understand what the calculator is actually doing — the resting-burn formula, the activity multiplier, a full worked example, and the honest limits of the estimate.

What TDEE actually is

TDEE isn’t a single mechanism — it’s the sum of four things your body spends energy on every day:

Basal metabolic rate (BMR): the calories you’d burn lying still all day just keeping the lights on — heartbeat, breathing, brain, organs. This is the biggest slice, usually 60–70% of the total.
Physical activity: deliberate exercise — the gym, a run, a bike ride.
The thermic effect of food (TEF): the energy it costs to digest and process what you eat, roughly 10% of your intake.
Non-exercise activity thermogenesis (NEAT): everything else you move for — walking, fidgeting, standing, chores. This varies enormously between people.

Add them up and you get your maintenance calories: eat that amount and your weight holds steady. The reason TDEE is the anchor for any goal is simple — a deficit or surplus only means anything as a distance from this number.

The Mifflin-St Jeor equation

To estimate TDEE you first estimate the biggest piece, BMR, then scale it up for activity. The most validated tool for the first step is the Mifflin-St Jeor equation, published in the American Journal of Clinical Nutrition in 1990. Its authors measured resting energy expenditure directly (by indirect calorimetry) in 498 healthy adults and fit an equation to the data. It predicts measured resting energy within about 10% for the majority of healthy, non-obese people — better than the older Harris-Benedict formula it largely replaced.

The equation uses weight in kilograms, height in centimeters, and age in years:

Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5 Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161

The only difference between the two is the final constant: +5 for men, −161 for women, which accounts for average differences in body composition.

A worked example

Take a 35-year-old woman who is 165 cm tall (about 5’5“) and weighs 75 kg (about 165 lb). Plug her into the women’s equation:

10 × 75 = 750
6.25 × 165 = 1,031.25
5 × 35 = 175
Constant: −161

BMR = 750 + 1,031.25 − 175 − 161 = ≈ 1,445 calories/day

That’s her resting burn. Now she needs to scale it up for how active she actually is. She works a desk job and does light exercise two or three days a week, which puts her in the “lightly active” band with a multiplier of 1.375:

TDEE = BMR × activity multiplier = 1,445 × 1.375 ≈ 1,987 calories/day

So her maintenance is roughly 2,000 calories. If her goal were fat loss, she’d set her deficit below that anchor — not below some generic “1,500 calories for women” number that has nothing to do with her body.

The activity multipliers

The second step — turning BMR into TDEE — comes down to picking the right multiplier. These are the standard values:

Activity level	Description	Multiplier
Sedentary	Little or no exercise, desk job	1.2
Lightly active	Light exercise 1–3 days/week	1.375
Moderately active	Moderate exercise 3–5 days/week	1.55
Very active	Hard exercise 6–7 days/week	1.725
Extra active	Hard daily exercise plus a physical job	1.9

Here is the single most useful piece of advice about this table: most people overestimate their activity level. It feels good to call yourself “very active,” but 1.725 assumes something close to two hours of hard training a day, and 1.9 assumes that plus a physically demanding job. Choose the multiplier that describes your typical week, not your best week. When you’re on the fence between two bands, take the lower one — it’s far easier to eat a little more later than to wonder why a “deficit” isn’t producing any loss. The 1.725 and 1.9 rows are where the biggest errors creep in.

Why it’s an estimate, not a measurement

TDEE from a formula is an educated approximation, and it’s worth holding it loosely. The Mifflin-St Jeor equation itself lands within roughly 10% for most healthy people — which on a 2,000-calorie maintenance means a real range of something like 1,800 to 2,200. The activity multiplier adds more uncertainty on top of that, because NEAT and true training intensity are hard to pin to a single number.

The practical fix is to treat the calculated figure as a starting point, then let the scale and the mirror correct it over a few weeks. If you eat at your estimated maintenance and weight trends down, your real TDEE was higher than the estimate; if it trends up, it was lower. Adjust from there.

One more thing that trips people up: TDEE drops as you lose weight. A smaller body burns fewer calories at rest and moves less mass around, so the same activity costs less. That’s why a deficit that worked at the start can stall months later — the maintenance number you were subtracting from has quietly shrunk. Recalculate every 4–5 kg (roughly 10 lb) of change so your targets keep pace.

Why this matters — especially on a GLP-1

Knowing your TDEE does two things at once. It sets the ceiling for a sensible deficit, and it sets the floor for protein. A common, evidence-aligned target is around 1.6 grams of protein per kilogram of body weight to protect lean mass while you’re eating less — a floor you can only set once you know where your calorie total sits.

That protein floor matters most for people losing weight fast, which is exactly the situation GLP-1 users are in. Rapid loss on these medications comes partly from muscle unless you deliberately protect it, as we cover in protecting lean mass on GLP-1s. And because scale weight alone can’t tell you whether you’re losing fat or muscle, it helps to pair your TDEE with a body-composition estimate — the Navy body fat method is a simple tape-measure approach for that.

The takeaway

TDEE is the sum of your resting burn, your activity, the cost of digesting food, and your everyday movement — and it’s the number every calorie goal is measured against. Estimate the resting piece with Mifflin-St Jeor, scale it with an honest activity multiplier (err low), and treat the result as a well-informed starting point that you refine from real-world results and recalculate as your weight changes. Run your own numbers through the TDEE & Macro Calculator to get your maintenance calories and a protein floor in one step. This is educational information, not medical or nutrition advice — talk to a clinician or dietitian before making significant changes to how you eat.