GuideJUNE 10, 2026~4 MIN

How to calculate TDEE and set up a realistic calorie deficit

The Mifflin-St Jeor formula, activity multipliers and worked examples - plus how to correct the formula's error against your own weight trend.

The short answer

Calculate TDEE by computing your BMR with the Mifflin-St Jeor formula (10 x weight kg + 6.25 x height cm - 5 x age, +5 for men or -161 for women) and multiplying by an activity factor between 1.2 and 1.9. For sustainable fat loss, eat 300-500 kcal below that number, which produces roughly 0.3-0.5 kg of loss per week.

This is the full method: the formula, worked examples, deficit sizing, and how to correct the result with your own weight data. If you just want the typical range for someone your age and sex, how many calories do you need per day? is the short answer — and the calorie calculator runs this maths for you in under a minute.

BMR (Basal Metabolic Rate): the energy your body burns at complete rest — keeping organs running, tissue maintained, temperature stable.

TDEE (Total Daily Energy Expenditure): BMR plus everything else — daily movement, exercise, and digestion. This is the number your calorie target should be set against.

Calorie deficit: eating below TDEE. The gap, accumulated over time, is what produces weight loss at roughly 7,700 kcal per kilogram of body fat.

Step 1 — BMR with Mifflin-St Jeor

The Mifflin-St Jeor equation is the standard formula for estimating BMR from body stats, and validation studies have repeatedly found it the most accurate of the common equations for modern populations:

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

Example: a 30-year-old woman, 70 kg, 168 cm → 700 + 1,050 − 150 − 161 = 1,439 kcal BMR.

Step 2 — multiply by an honest activity factor

Lifestyle	Multiplier	Description
Sedentary	1.2	Desk job, little deliberate exercise
Lightly active	1.375	Exercise 1–3 days/week
Moderately active	1.55	Exercise 3–5 days/week
Very active	1.725	Hard exercise 6–7 days/week
Extremely active	1.9	Physical job plus training

The classic mistake is optimism: three gym sessions a week on top of a desk job is "lightly active", not "moderately". Most people with office jobs and regular exercise sit between 1.375 and 1.55. Our example at 1.375: 1,439 × 1.375 ≈ 1,979 kcal TDEE.

Step 3 — choose a deficit that survives contact with real life

Deficit	Weekly loss (approx.)	Verdict
200–300 kcal/day	~0.2–0.3 kg	Gentle — good for the last few kilos
300–500 kcal/day	~0.3–0.5 kg	The sustainable sweet spot for most people
500–750 kcal/day	~0.5–0.7 kg	Workable with higher body weight and good protein
1,000+ kcal/day	~1 kg+	Usually collapses — hunger, muscle loss, rebound

The conversion: each 0.1 kg of fat is ~770 kcal, so a 440 kcal daily deficit is ~0.4 kg per week. Aggressive deficits look efficient on paper and fail statistically — adherence, not ambition, is the variable that predicts outcomes. Our example person cutting 450: target ≈ 1,530 kcal/day, on track for ~2 kg/month. During any deficit, keep protein around 1.6–2.2 g per kg of body weight to protect muscle.

Step 4 — the formula got you close; your scale makes it exact

Mifflin-St Jeor carries a ±10–15% error bar for individuals — for our example, roughly ±200–300 kcal/day, which can be most of the planned deficit. The fix isn't a better formula; it's feedback. Log your intake and your morning weight for 2–3 weeks, then compare:

Losing as planned → your TDEE estimate was right. Change nothing.
Trend flat → your true TDEE is lower than estimated. Your logged average intake IS your maintenance; subtract the deficit from that instead.
Losing much faster than planned → true TDEE is higher; eat a little more and keep the loss at a rate you can sustain.

Every 0.1 kg/week of unexplained difference equals about 110 kcal/day of estimation error. This calibration loop is why Calorie.one keeps the food log and the weight trend in one place — and its free calorie calculator runs exactly the math above to give you a starting target, no account required.

FAQ

What's the difference between BMR and TDEE?

BMR is your energy burn at complete rest; TDEE adds all movement and digestion on top. Never eat below your BMR as a routine strategy — deficits are taken from TDEE, and BMR is typically only 60–75% of it.

Should I eat back exercise calories?

If your activity multiplier already includes your training, no — that would double-count. Only add calories for genuinely unusual activity (a race day, a long hike) beyond what your multiplier assumed. Fitness-tracker exercise calorie estimates also run high, often by 20% or more.

Why has my weight loss stopped after a few months?

Two honest reasons: you weigh less, so your TDEE genuinely dropped (recalculate with your new weight — a 10 kg loss lowers TDEE by roughly 100–200 kcal/day), and logging drift, where untracked bites creep back in. Recalculate, tighten the log for two weeks, and only then consider a further cut.

How fast can I lose weight safely?

0.5–1% of body weight per week is the range most evidence supports for preserving muscle and adherence; for most people that's 0.3–0.8 kg. Faster than that on a sustained basis usually costs muscle, energy and — via rebound — the result itself.