What is a calorie deficit?

A calorie deficit is eating fewer calories than your body burns. Over time this forces your body to use stored energy — primarily body fat — to make up the difference.

How big a deficit is safe?

A deficit of 300–550 kcal/day is sustainable for most people and targets 0.25–0.5 kg (0.5–1 lb) of loss per week. Larger deficits work short-term but are harder to maintain and can lead to muscle loss.

Why is 3,500 kcal ≈ 1 lb of fat?

One pound of body fat stores roughly 3,500 kcal of energy. It's a useful rule of thumb, though real-world loss is affected by water, glycogen, muscle, and metabolic adaptation.

Will I lose muscle in a deficit?

You can minimise muscle loss by keeping protein high (1.6–2.4 g/kg), doing resistance training, and avoiding very aggressive deficits. See the protein calculator for a target.

Why does my target stop going down?

Daily intake is held at a 1,200 cal/day floor. Below that it gets hard to meet basic protein, vitamin, and mineral needs, so a faster pace is capped rather than shown — talk to a clinician if you are considering going lower.