What is a Calorie Deficit? (And Why Most People Get It Wrong)

You've probably heard that fat loss requires a calorie deficit. Eat less than you burn, and you'll lose weight.

Simple, right?

Except most people get it wrong. They either create too large a deficit (and burn out). Or they create too small a deficit (and don't lose weight). Or they don't actually create a deficit at all (and wonder why they're not losing weight).

Let me explain how to do it right.

What is a Calorie Deficit?

A calorie deficit is simple: you eat fewer calories than your body burns.

Your body burns calories three ways:

1. Basal Metabolic Rate (BMR): The calories you burn just existing (breathing, thinking, keeping your heart beating). This is roughly 60–70% of your total daily energy expenditure.

2. Thermic Effect of Food (TEF): The calories you burn digesting food. This is roughly 10% of your total daily energy expenditure.

3. Activity Energy Expenditure (AEE): The calories you burn through exercise and daily movement. This is roughly 20–30% of your total daily energy expenditure.

Add these three together and you get your Total Daily Energy Expenditure (TDEE). This is how many calories you burn per day.

A calorie deficit means eating less than your TDEE. So if your TDEE is 2,500 calories, eating 2,000 calories puts you in a 500-calorie deficit.

When you're in a calorie deficit, your body has to use stored energy (fat) to make up the difference. So you lose weight.

Why Most People Get It Wrong

Here's where most people mess up:

They don't actually know their TDEE. They read some article, plug their stats into a calculator, and get a number. Then they assume that number is accurate. It's not. Online calculators are rough estimates. Your actual TDEE depends on your individual metabolism, activity level, and body composition.

They create too large a deficit. They think "if 500 calories is good, 1,000 must be better." So they eat 1,000 calories below their maintenance. They lose weight fast. But they're hungry, exhausted, and miserable. They burn out after a few weeks and give up.

They don't track accurately. They think they're in a deficit, but they're not tracking their food accurately. They're underestimating portion sizes. They're forgetting about drinks and snacks. So they're not actually in a deficit.

They don't adjust based on results. They create a deficit, but they don't track their progress. If they're not losing weight after two weeks, they don't know if they need to drop their calories more or if they're actually in a deficit.

How to Create the Right Calorie Deficit

Here's how to do it correctly:

Step 1: Estimate your TDEE. Multiply your body weight (in pounds) by 14–16. This is a rough estimate of your daily calorie burn. So if you weigh 200lbs, your TDEE is roughly 2,800–3,200 calories.

Step 2: Create a moderate deficit. Subtract 300–500 calories from your estimated TDEE. So if your TDEE is 2,800, eat 2,300–2,500 calories per day.

Step 3: Track your food accurately. Use a food scale. Log everything in an app like MyFitnessPal. Do this for at least two weeks.

Step 4: Track your progress. Weigh yourself daily (or every few days) and track the average. Take progress photos. Measure your waist.

Step 5: Adjust based on results. If you're losing 0.5–1lb per week, you're in the right deficit. If you're losing more than 1lb per week, you might be in too large a deficit. If you're not losing weight, drop your calories by 200 and try again.

That's it. That's how you create the right calorie deficit.

Why a Moderate Deficit Works Better Than an Extreme Deficit

An extreme deficit (1,000+ calories below maintenance) will make you lose weight faster. But it has problems:

You'll be hungry. Your body will fight back with increased hunger hormones. You'll crave food constantly.

You'll be exhausted. Your energy will tank. You won't have energy for workouts. You won't have energy for life.

You'll lose muscle. A large deficit causes your body to break down muscle for energy. You'll lose fat, but you'll also lose muscle. This makes you look worse when you lose weight.

You'll burn out. You can't sustain an extreme deficit. You'll white-knuckle through it for a few weeks, then give up and binge.

A moderate deficit (300–500 calories below maintenance) works better because:

You won't be as hungry. A moderate deficit is sustainable. You can stick with it.

You'll have energy. You can still do your workouts. You can still function normally.

You'll preserve muscle. A moderate deficit, combined with strength training and adequate protein, preserves muscle. You'll lose fat, not muscle.

You can stick with it. This is the most important factor. A moderate deficit is sustainable long-term.

Real Client Example

Here's a real example (name changed for privacy):

Tom is a 40-year-old manager in Glasgow. He weighs 220lbs. We estimated his TDEE at 3,000 calories (220 × 14).

We put him in a 400-calorie deficit. He ate 2,600 calories per day.

He lost 0.75lbs per week. After 12 weeks, he lost 9 pounds.

He wasn't hungry. He had energy. He did his workouts. He stuck with it.

That's how it works.

What You Need to Do Right Now

If you want to create the right calorie deficit, here's your action plan:

Step 1: Estimate your TDEE (body weight × 14–16).

Step 2: Create a moderate deficit (300–500 calories below TDEE).

Step 3: Track your food accurately for two weeks.

Step 4: Track your progress (weight, photos, measurements).

Step 5: Adjust based on results.

That's it. You're in a calorie deficit.