What is a calorie deficit?
A calorie deficit means your energy intake is below your total daily energy expenditure. To cover the gap, your body draws on stored energy — mostly fat, but also some muscle if protein and training are insufficient.
A common rule of thumb is that about 7,700 kcal equals 1 kg of body weight (≈3,500 kcal per pound). In practice weight loss slows over time because your energy needs fall as you get lighter, so recalculate every few kilograms.
How big should the deficit be?
Most adults do well with a deficit of 15–25% below maintenance, or a loss of 0.5–1% of body weight per week. Our tools cap the deficit at 25% of your TDEE (and 1,000 kcal/day) and never recommend less than a safe calorie floor.
- Small deficit (~10–15%): slower, easiest to sustain, best for lean people.
- Moderate deficit (~20–25%): a good default for most people.
- Aggressive deficits: more hunger, fatigue and muscle loss — only with professional supervision.
Protect your muscle
Keep protein high — roughly 1.6–2.2 g per kg of body weight per day — and keep lifting weights. Strength training tells your body the muscle is still needed, and adequate protein supplies the building blocks.
Maintain your training intensity (the weights you lift) even if you reduce the total number of sets.
Make it sustainable
Prioritise high-volume, high-fibre foods such as vegetables, fruit, legumes and lean proteins; they help control hunger. Plan meals ahead, sleep 7–9 hours and allow flexibility — adherence over months beats perfection over days.
Frequently asked questions
Why did my weight loss stall?
As you lose weight your maintenance calories fall, and water retention can mask fat loss for a week or two. Recalculate your needs and look at 2–3 week averages before cutting further.
Is a 1,000-calorie deficit safe?
For many people it is too aggressive. Our calculator limits the deficit to 25% of your estimated expenditure and never goes below a minimum intake.
Do I need to do cardio to lose fat?
No — the deficit can come from diet alone — but regular activity improves health and makes the deficit easier to maintain.
