# Calorie deficit, explained > A calorie deficit means eating fewer calories than you burn, which forces your body to use stored fat for energy. A moderate deficit of about 10–20% below maintenance — roughly a 300–600 kcal daily shortfall — loses fat steadily while protecting muscle. Track the weekly weight trend and adjust as maintenance falls. Source: Lift Republic (https://liftrepublic.com/learn/calorie-deficit-explained) Category: Fat loss · Published: 2026-06-04 · Reviewed: 2026-06-04 A calorie deficit is the one thing every fat-loss diet has in common, whatever its name. Understand it and you no longer need the gimmicks. ## What a calorie deficit actually is Your body burns a certain number of calories each day — your [maintenance calories](/tools/tdee), or TDEE. Eat fewer than that and you're in a **deficit**: your body makes up the shortfall by using stored energy, mostly fat. Eat more and you're in a surplus. That's the whole mechanism. Roughly **7,700 kcal** equals about 1 kg of body fat, so a 500 kcal daily deficit loses around 0.45 kg a week. ## How big should it be? Bigger is not better. A **moderate deficit of 10–20% below maintenance** — usually a 300–600 kcal daily shortfall — is the sweet spot: - Large enough to lose fat steadily (about **0.5–1% of bodyweight per week**). - Small enough to protect muscle, training performance and your sanity. Aggressive crash deficits cost muscle, tank your energy and almost always rebound. Work out your target below. [[calc:calorie-target]] ## How to create the deficit You can eat less, move more, or both — but **diet is the powerful lever**: - Build meals around **protein and whole foods**, which are filling for their calories. - Keep protein high (around 2 g per kg) to protect muscle — see [how much protein to build muscle](/learn/how-much-protein-to-build-muscle). - Use steps and training to spend energy and stay healthy, not to "earn back" food. ## Track the trend, not the day Bodyweight swings daily with water, food and salt. What matters is the **multi-week trend**. Weigh in consistently, watch the average, and only cut calories further when the trend stalls for 2–3 weeks — because as you lose weight, your maintenance falls too. This is exactly where data-driven coaching earns its place: our [fat-loss programme](/programmes/fat-loss) and [nutrition coaching](/nutrition) recalibrate your deficit from your real trend, so you keep losing without guessing. Want it done for you? [Start with nutrition](/nutrition). ## FAQ ### What is a calorie deficit? A calorie deficit is eating fewer calories than your body burns in a day. With less incoming energy, your body draws on stored fat to make up the difference — which is how fat loss happens. ### How big should my calorie deficit be? A moderate deficit of about 10–20% below your maintenance calories — often a 300–600 kcal daily shortfall — is the sweet spot. It's large enough to progress but small enough to protect muscle, energy and adherence. ### Why am I in a deficit but not losing weight? Usually water retention, an inaccurate calorie estimate, or maintenance falling as you lose weight. Judge progress on the 2–3 week trend, not the daily scale, and recalibrate when the trend genuinely stalls.