Calorie Deficit Explained: How Much Should You Really Eat?

A calorie deficit is the single mechanism behind every successful fat loss plan ever — keto, IIFYM, intermittent fasting, Weight Watchers, carnivore, vegan. They all work for one reason only: they get you eating less energy than your body burns. The interesting question isn't whether you need a deficit. It's how big a deficit you can run before it starts costing you muscle, mood, sleep and training quality.

This guide walks through exactly how to calculate your maintenance calories, choose a deficit size that fits your life, hit your protein target, and adjust when progress slows. Everything here is the same logic Calorie Compass uses under the hood — just laid out so you can see it.

What a calorie deficit actually is

Your body burns energy 24 hours a day to keep your heart beating, your brain thinking and your muscles moving. That total daily energy expenditure (TDEE) is made up of four parts: your basal metabolic rate (BMR, ~60–70%), the thermic effect of food (TEF, ~10%), exercise activity (EAT, ~5–15%) and non-exercise activity (NEAT — fidgeting, walking, standing, ~15–30%).

Eat less than that total and your body makes up the difference by burning stored energy — mostly fat, plus a small amount of muscle if protein and training are neglected. That's it. There is no metabolic trick, food combination or supplement that bypasses this.

Step 1 — Find your maintenance calories

The Mifflin-St Jeor equation is the most accurate predictive formula for healthy adults. It estimates your BMR — what you'd burn lying in bed all day — and then you multiply by an activity factor.

• Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
• Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
• Sedentary desk job × 1.2
• Light activity (1–3 sessions/week) × 1.375
• Moderate activity (3–5 sessions/week) × 1.55
• Very active (6+ sessions/week or physical job) × 1.725

Step 2 — Choose a deficit you can sustain

The sweet spot for almost everyone is a 10–20% deficit below maintenance. That usually translates to 0.4–0.8 kg of fat loss per week, preserves muscle, and doesn't trash your energy or training. Bigger deficits look attractive on paper but the dropout rate is brutal.

• 10% deficit — slow, easy, ideal if you're already lean or have lots of time
• 15% deficit — the default that works for most people
• 20% deficit — aggressive but doable for 8–12 weeks max
• 25%+ deficit — only with medical supervision or genuinely high body fat

Step 3 — Lock in your protein

Protein is the most important macro in a deficit. It preserves the muscle you've built, keeps you full for longer than carbs or fat, and has the highest thermic effect (your body burns ~25% of the calories in protein just digesting it).

Aim for 1.6–2.2 g of protein per kg of bodyweight. Higher end if you're leaner, training hard, or older. A 70 kg lifter should be hitting 112–155 g per day — roughly 30–40 g per meal across 3–4 meals.

Step 4 — Track, weigh, adjust

1. 1Weigh yourself daily, first thing, after the bathroom, before food.
2. 2Average those readings across the week — the daily number means almost nothing on its own.
3. 3After 2–3 weeks, compare the weekly average to your starting weight.
4. 4If you've lost 0.4–0.8% of bodyweight per week, do nothing. Keep going.
5. 5If the scale hasn't moved in 2+ weeks, drop calories by 100–150 or add 1,500 daily steps.

Common mistakes that stall progress

• Cutting too aggressively (>25% below maintenance) and binging on the weekend
• Forgetting that weight is non-linear — water, sodium, glycogen and digestion swing it 1–2 kg daily
• Underestimating liquid calories (coffees, juice, alcohol) — easily 300–600 kcal/day
• Not adjusting after 4–6 weeks of progress, then blaming 'metabolic damage'
• Eating perfectly Monday–Friday and undoing it all on the weekend

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