Calorie Deficit Explained: How to Lose Weight Without Losing Your Mind

Every weight loss method — keto, paleo, intermittent fasting, veganism, carnivore — works through exactly one mechanism: a calorie deficit. Eat fewer calories than your body burns, and you lose weight. Eat more, and you gain.

This isn’t opinion. It’s thermodynamics. The question isn’t whether a calorie deficit works — it’s how to create one that’s sustainable without making you miserable.

What Is a Calorie Deficit?

A calorie deficit is the gap between the energy your body uses and the energy you consume from food.

Your body burns calories in three ways:

1. Basal Metabolic Rate (BMR): The calories your body burns just existing — breathing, pumping blood, maintaining body temperature. This accounts for 60–70% of total daily expenditure for most people.

2. Thermic Effect of Food (TEF): The energy it takes to digest food. Protein has the highest thermic effect (~20–30%), meaning your body burns more calories digesting protein than carbs or fats.

3. Activity: Everything from walking to the shops to an hour of weightlifting. This is the most variable component.

Add these together and you get your Total Daily Energy Expenditure (TDEE). If you eat less than your TDEE, you’re in a deficit. If you eat more, you’re in a surplus.

How to Calculate Your Calorie Deficit

Step 1: Find Your TDEE

The most accurate way without laboratory equipment is the Mifflin-St Jeor equation, which calculates your BMR and multiplies it by an activity factor.

You can do this instantly with our free macro calculator — just enter your age, weight, height, activity level, and goal.

For reference, the formulas are:

• Males: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
• Females: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Multiply by your activity level (1.2 for sedentary, up to 1.9 for very active) to get TDEE.

Step 2: Subtract to Create a Deficit

A deficit of 500 calories per day produces roughly 0.5kg (1lb) of fat loss per week. This is the rate most nutrition experts recommend — fast enough to see results, slow enough to preserve muscle.

Deficit Size	Weekly Loss	Best For
250 kcal/day	~0.25kg/week	Lean people, slow recomp
500 kcal/day	~0.5kg/week	Most people, sustainable
750 kcal/day	~0.75kg/week	Higher body fat, short-term
1000+ kcal/day	~1kg/week	Not recommended for most

Warning: Deficits larger than 500–750 calories increase muscle loss, crash your energy, and are harder to sustain. Aggressive diets work faster initially but almost always lead to rebound weight gain.

Step 3: Set Your Macros

A calorie deficit tells you how much to eat. Macros tell you what to eat. Within your calorie target, aim for:

• Protein: 1.6–2.2g per kg bodyweight (protects muscle in a deficit)
• Fats: 20–30% of total calories (hormones, absorption, satiety)
• Carbs: Whatever’s left (fuel for training and daily function)

Our macro calculator does this split automatically.

Common Calorie Deficit Mistakes

1. The Deficit Is Too Aggressive

Eating 1,200 calories when your TDEE is 2,400 feels productive — but your body fights back. Metabolic adaptation kicks in, hunger skyrockets, and you’re one bad day away from a binge that wipes out a week’s worth of deficit.

Fix: Start with a 500-calorie deficit. Increase it slightly only if progress stalls after 2–3 weeks.

2. Not Eating Enough Protein

In a deficit, your body needs a reason to keep muscle. Protein gives it that reason. Without adequate protein, you’ll lose weight — but a significant portion will be muscle, not fat.

Fix: Aim for at least 1.6g protein per kg bodyweight. Track it.

3. Not Actually Tracking

“I’m eating healthy but not losing weight” almost always means the person is eating more than they think. Studies consistently show people underestimate calorie intake by 20–50%.

Fix: Track your food for at least 2 weeks. You don’t need to do it forever, but you need to calibrate your intuition. Tools like Chowdown make this painless — snap a photo and the AI calculates your macros automatically.

4. Weekend Calories Don’t Count (They Do)

A perfect 500-calorie deficit Monday through Friday (2,500 deficit) gets wiped by one big Saturday dinner and a Sunday brunch (easily 2,000+ surplus over two days). The maths works on weekly averages, and weekends count.

Fix: You don’t need to be perfect on weekends, but you need to be aware. Track your food on Saturdays and Sundays too — even roughly.

5. Relying Only on the Scale

Weight fluctuates daily by 1–3kg from water retention, food volume, sleep quality, stress, and menstrual cycles. If you weigh yourself daily and panic at fluctuations, you’ll quit.

Fix: Weigh yourself daily but look at the weekly average. If your 7-day average is trending down, you’re losing fat — regardless of what any single day shows.

6. Eliminating Food Groups Unnecessarily

You don’t need to cut carbs, eliminate gluten, avoid dairy, or stop eating after 6pm to be in a deficit. These restrictions make dieting harder without making it more effective.

Fix: Focus on the calorie target and protein target. Everything else is optional. Read about flexible dieting (IIFYM) for a sustainable approach.

How Long Should You Stay in a Deficit?

Sustained calorie restriction for months on end isn’t ideal. After 8–12 weeks of dieting, consider a “diet break” — eating at maintenance for 1–2 weeks before resuming.

Research suggests diet breaks improve adherence, reduce metabolic adaptation, and lead to the same total fat loss over time compared to continuous dieting.

A reasonable approach:

1. Weeks 1–10: Moderate deficit (–500 kcal)
2. Weeks 11–12: Diet break (eat at maintenance TDEE)
3. Repeat if you have more to lose

The Role of Exercise in a Calorie Deficit

Exercise helps create a deficit, but it’s much less efficient than most people think:

• Running for 30 minutes burns roughly 300 calories
• A chocolate bar has roughly 250 calories

You can’t outrun a bad diet. Exercise is important for health, fitness, and muscle retention — but the deficit itself should come primarily from food.

That said, resistance training is non-negotiable during a deficit. It’s the strongest signal you can give your body to preserve muscle. Even 2–3 sessions per week makes a significant difference.

Free Tools to Make It Work

You don’t need expensive apps or meal delivery services to maintain a calorie deficit. Here’s everything you need, completely free:

1. Chowdown Macro Calculator — Calculate your TDEE and deficit targets
2. Chowdown App — Track your food by snapping photos. AI handles the calorie counting
3. A bathroom scale — Weigh daily, track weekly averages
4. A tape measure — Track waist circumference monthly (more reliable than weight alone)

The Bottom Line

A calorie deficit is simple in concept and challenging in execution. But it doesn’t have to be miserable. Set a moderate deficit, eat enough protein, track your food consistently, and be patient.

The people who succeed at losing weight aren’t the ones who find the most aggressive diet — they’re the ones who find an approach they can stick to for months.

Start with our free macro calculator to get your numbers, then use Chowdown to track your food effortlessly. Both completely free, forever.