How to Calculate Calories for Weight Loss or Gain — TDEE Explained
The energy balance principle
Body weight tracks energy balance: calories in versus calories out. Eat below expenditure and the body draws on stored energy; eat above it and surplus is stored. The calculation answers one question — what is your out?
Step 1: BMR (basal metabolic rate)
Mifflin-St Jeor (women): BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161
Step 2: TDEE (apply activity factor)
| Lifestyle | Factor |
|---|---|
| Sedentary (desk job, little exercise) | 1.2 |
| Light (1–3 workouts/week) | 1.375 |
| Moderate (3–5 workouts/week) | 1.55 |
| Very active (6–7 workouts/week) | 1.725 |
| Athlete / physical job | 1.9 |
Step 3: apply the goal
- Fat loss: TDEE − 300 to 500 kcal (≈0.25–0.5 kg/week)
- Maintenance: TDEE
- Muscle gain: TDEE + 200 to 300 kcal (limiting fat gain)
Full worked example
Male · 30 years · 80 kg · 178 cm · moderate activity
BMR = 10×80 + 6.25×178 − 5×30 + 5 = 800 + 1112.5 − 150 + 5 = 1,767.5
TDEE = 1,767.5 × 1.55 ≈ 2,740 kcal
Fat loss target = 2,740 − 500 ≈ 2,240 kcal/day (≈0.45 kg/week)
Reading the scale correctly
- Week 1: much of early loss is water/glycogen — don't extrapolate.
- Weekly average vs daily weight: fluctuations of ±1–2 kg are normal from salt, carbs and hormones.
- Recheck monthly: as weight drops, TDEE drops — recalculate every 4–6 weeks.
Common mistakes
- Overestimating activity level — most people should start one tier lower than feels right.
- Counting exercise calories twice (activity factor + separate burn credits).
- Crash dieting below BMR for extended periods — adaptation makes regain likely.
- Ignoring protein and strength training, which protect muscle in a deficit.
Why the multiplier is the weakest link (and how to fix it)
Every number in the chain above is a measured regression — except the activity multiplier, which is a guess you make about yourself. The gap between tiers is enormous: for the worked example's BMR of 1,767.5, moving from 1.375 to 1.55 swings TDEE by 310 kcal/day — the entire intended deficit, created by one honest-vs-optimistic self-assessment. This is why "I'm eating less and not losing" so often traces to a multiplier chosen one tier too high, then exercise calories counted on top of it (double-counting — mistake #2 below).
The fix is calibration, not precision: treat the computed TDEE as a hypothesis, hold intake steady at it for 2–3 weeks while recording weekly average weight, then adjust by what happened. Weight held flat → that number was your TDEE, whatever the table said. Lost 0.4 kg/week → you were eating ~1,900 below true expenditure, and the deficit is bigger than intended. Two calibration cycles teach you more about your metabolism than any formula refinement — the calorie calculator gives the starting hypothesis, the record-keeping converts it to a fact.
Macros: turning calories into grams
Once the calorie target exists, macro targets are simple division — protein and carbs carry 4 kcal/g, fat 9 kcal/g. For an 80 kg lifter holding muscle on a 2,600 kcal target with a 30/40/30 split:
Protein: 2,600 × 0.30 ÷ 4 = 195 g (2.4 g/kg — training-day appropriate)
Carbs: 2,600 × 0.40 ÷ 4 = 260 g · Fat: 2,600 × 0.30 ÷ 9 ≈ 87 g
The split is a preference dials, not a law: protein anchored at 1.6–2.2 g/kg, fat above ~0.5 g/kg for hormones, and carbs filling the remainder is the standard, evidence-consistent approach. Precision beyond that earns nothing measurable — adherence does the work.
Health note: Formulas are population averages; individual metabolism varies. If you are under 18, pregnant, managing a medical condition, or have a history of disordered eating, work with a qualified professional rather than a formula.
FAQ
Do I need to hit macros exactly?
Calories drive weight change; protein adequacy (roughly 1.6–2.2 g/kg) helps preserve muscle. Carb/fat split is mostly preference within your calorie target.
Why did weight loss stop after a few weeks?
Commonly: TDEE fell with body weight, activity dropped unconsciously, or water retention masks fat loss. Recalculate, track weekly averages, and give it 2–3 more weeks before adjusting.
Does eating late at night matter?
Total daily intake matters far more than timing for weight. Meal timing can affect adherence and sleep — both worth optimizing, but not the core math.