How to calculate a calorie deficit for steady weight loss

A calorie deficit is the foundation of every successful fat loss plan. No matter what diet you follow — low-carb, Mediterranean, intermittent fasting — they all work through the same mechanism: consuming fewer calories than you burn.

Here's how to calculate the right deficit for your body and make it sustainable.

What is a calorie deficit?

A calorie deficit occurs when you eat fewer calories than your body burns in a day (your TDEE). Your body then turns to stored energy — primarily body fat — to make up the difference. Over time, this results in fat loss.

Step 1: Find your TDEE

Before you can create a deficit, you need to know your maintenance calories — how many calories you burn on a typical day. This is your TDEE (Total Daily Energy Expenditure).

Your TDEE depends on your age, weight, height, sex, and activity level. The most accurate way to find it is to use a calculator based on the Mifflin-St Jeor equation.

Step 2: Choose your deficit size

Not all deficits are created equal. Here's a breakdown of common approaches:

• Small deficit (200–300 kcal/day): Very sustainable, minimal hunger, preserves muscle well. Expected loss: ~0.2–0.3 kg/week. Best for people close to their goal weight or those who struggle with hunger.
• Moderate deficit (400–500 kcal/day): The sweet spot for most people. Noticeable progress without excessive sacrifice. Expected loss: ~0.4–0.5 kg/week.
• Larger deficit (500–750 kcal/day): Faster results but harder to maintain. Higher risk of muscle loss if protein intake isn't high. Expected loss: ~0.5–0.75 kg/week.
• Aggressive deficit (750–1000 kcal/day): Only suitable short-term or under medical supervision. Risk of fatigue, muscle loss, nutrient deficiencies, and metabolic adaptation.

Step 3: Set a calorie floor

No matter what deficit you choose, there's a minimum below which you shouldn't go without medical guidance:

• Women: generally not below 1,200 kcal/day
• Men: generally not below 1,500 kcal/day

Going below these numbers risks nutrient deficiencies, hormonal disruption, and muscle breakdown — and makes the deficit unsustainable.

Why protein matters in a deficit

When you eat less, your body doesn't just burn fat — it can also break down muscle for energy, especially if your protein intake is low. To protect muscle mass during fat loss:

• Aim for 1.6–2.2g of protein per kg of bodyweight per day.
• Distribute protein across meals rather than consuming it all at once.
• Combine your deficit with resistance training to further protect and build muscle.

Common mistakes people make with calorie deficits

1. Underestimating calories eaten

Studies show people consistently underestimate their calorie intake by 20–40%. Sauces, oils, drinks, and snacks all add up. Using a food tracking app for even a few weeks dramatically improves accuracy.

2. Overestimating calories burned

Exercise machines and fitness trackers tend to overestimate calorie burn. Use exercise as a health tool, not a justification to eat significantly more.

3. Starting too aggressively

A very large deficit feels manageable for a week but leads to intense hunger, low energy, and eventual overeating. A moderate deficit you can sustain for months beats an extreme deficit you abandon in two weeks.

4. Not recalculating as weight drops

As you lose weight, your TDEE decreases. If you don't adjust, progress stalls. Recalculate every 4–6 weeks or when your weight drops by 3–5 kg.

How long will it take to reach your goal?

With a 500 kcal/day deficit, expect roughly 2 kg of fat loss per month. With a 300 kcal deficit, around 1.2 kg per month. These are averages — your actual results depend on consistency, water retention fluctuations, and how accurately you track.

Weight loss is rarely linear. Expect weeks where the scale doesn't move even if you're in a consistent deficit — water retention, hormonal fluctuations, and digestive content all affect daily weight. Judge progress over 2–4 week trends, not day-to-day.

Key takeaways

• Find your TDEE first, then subtract 300–500 calories to create a sustainable deficit.
• Don't go below 1,200 kcal (women) or 1,500 kcal (men) without medical guidance.
• Eat enough protein (1.6–2.2g/kg) to preserve muscle during fat loss.
• Track intake honestly — most people underestimate what they eat.
• Recalculate your targets as your weight changes.