What is a calorie deficit?
A calorie deficit occurs when you consume fewer calories than your body expends in a given period. Your Total Daily Energy Expenditure (TDEE) is the total number of calories you burn in a day — through your resting metabolism, movement, exercise, and digestion.
When you eat below your TDEE, your body must draw on stored energy — primarily body fat — to make up the difference. That's weight loss at its most basic level.
📐 The fundamental equation
Calorie deficit = TDEE − calories consumed
A deficit of ~3,500 calories equals approximately 0.45 kg (1 lb) of fat loss — though this is a rough estimate, not a precise rule.
How large should your deficit be?
This is where most people get it wrong. Bigger deficit ≠ better results. An aggressive deficit accelerates muscle loss, causes hormonal disruption, and is nearly impossible to sustain.
| Deficit size | Weekly loss (est.) | Best for | Risk |
|---|---|---|---|
| 250 kcal/day | ~0.25 kg / 0.5 lb | Slow, sustainable loss | Very low |
| 500 kcal/day | ~0.5 kg / 1 lb | Most people — recommended starting point | Low |
| 750 kcal/day | ~0.75 kg / 1.5 lb | Higher body fat, with high protein | Moderate |
| 1,000 kcal/day | ~1 kg / 2 lb | Short-term, medically supervised only | High |
For most people, a 400–500 kcal/day deficit hits the sweet spot: fast enough to see real progress, slow enough to preserve muscle and maintain energy.
Step-by-step: calculate your deficit
Step 1: Find your TDEE
Your TDEE is your maintenance calorie level — eat at this number and your weight stays stable. The most common way to estimate it is with the Mifflin-St Jeor formula for BMR, then multiply by an activity factor:
- Sedentary (little exercise): BMR × 1.2
- Lightly active (1–3 days/week): BMR × 1.375
- Moderately active (3–5 days/week): BMR × 1.55
- Very active (6–7 days/week): BMR × 1.725
- Athlete / physical job: BMR × 1.9
Step 2: Set your deficit
Subtract 400–500 kcal from your TDEE. Example: TDEE of 2,400 kcal → target intake of 1,900–2,000 kcal/day.
Step 3: Set a high protein target
During a deficit, muscle preservation requires adequate protein. Aim for 1.8–2.2g of protein per kg of body weight. Protein also increases satiety, making the deficit easier to sustain.
Step 4: Track and adjust
After 2–3 weeks, check your rate of loss. If you're losing faster than 1 kg/week without strength training, increase calories slightly. If nothing is happening, reduce by 100–150 kcal. Your TDEE estimate may not be perfect — real-world feedback matters more than the formula.
Common mistakes with calorie deficits
- Cutting too aggressively: Deficits over 1,000 kcal/day cause disproportionate muscle loss and metabolic adaptation.
- Not tracking accurately: Studies show people underestimate food intake by 20–40%. Weighing food (not just measuring volume) dramatically improves accuracy.
- Ignoring protein: Low protein during a deficit is the fastest way to lose muscle instead of fat.
- Not adjusting over time: As you lose weight, your TDEE drops. Recalculate every 4–6 weeks.
- Weekend overeating: A 500 kcal/day deficit Mon–Fri can be erased by a 1,750 kcal surplus over the weekend.
Calculate your TDEE and get a personalised calorie target in under a minute.
Calculate my TDEE →What to do when you hit a plateau
Weight loss plateaus happen to almost everyone. Your body adapts to a lower calorie intake by reducing NEAT (non-exercise activity thermogenesis) — unconscious movement like fidgeting, posture shifts, and walking pace. This is called metabolic adaptation.
Options when you plateau: take a 1–2 week "diet break" at maintenance calories (which partially reverses adaptation), slightly reduce calories by 100–150 kcal, or increase activity rather than cutting more food.