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How to Calculate Your Calorie Deficit for Weight Loss

If you've ever felt overwhelmed by conflicting diet advice — keto, fasting, low-carb, "clean eating" — here's the one truth underneath all of it: you lose fat when you eat fewer calories than your body burns. That gap is called a calorie deficit, and it's the engine behind every successful diet, no matter the label.

The best part? Calculating your deficit is simple arithmetic. In a few minutes you'll know exactly how many calories to aim for. Let's do it.

What is a calorie deficit?

A calorie deficit is the difference between the calories you eat and the calories you burn. Burn more than you eat, and your body taps into stored fat to make up the difference. That's weight loss.

Roughly speaking, one pound of fat ≈ 3,500 calories. So a daily deficit of 500 calories adds up to about one pound of fat loss per week. That's the math we're going to personalize for you.

Step 1: Find your maintenance calories (TDEE)

Your TDEE (Total Daily Energy Expenditure) is how many calories you burn in a day — the number that keeps your weight stable. It has two parts:

  • BMR (Basal Metabolic Rate): the calories you burn just existing — breathing, pumping blood, staying warm.
  • Activity: everything on top — walking, working out, fidgeting, daily life.

A quick way to estimate your BMR is the Mifflin-St Jeor equation:

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

Then multiply BMR by an activity factor:

  • Sedentary (little exercise): × 1.2
  • Lightly active (1–3 days/week): × 1.375
  • Moderately active (3–5 days/week): × 1.55
  • Very active (6–7 days/week): × 1.725

The result is your TDEE — your maintenance calories.

Example: A 35-year-old woman, 70 kg, 165 cm, moderately active. BMR = (10 × 70) + (6.25 × 165) − (5 × 35) − 161 = 1,395. TDEE = 1,395 × 1.55 ≈ 2,160 calories/day.

Step 2: Subtract your deficit

Now choose how aggressive to be. A safe, sustainable deficit is usually 15–25% below maintenance, or a flat 300–700 calories:

  • Gentle (~0.5 lb/week): subtract ~250 calories
  • Moderate (~1 lb/week): subtract ~500 calories
  • Aggressive (~1.5 lb/week): subtract ~750 calories

Using our example (2,160 TDEE), a moderate 500-calorie deficit gives a target of ~1,660 calories/day.

Step 3: Don't go too low

It's tempting to slash calories hard, but crash deficits backfire:

  • You lose muscle along with fat.
  • Hunger and fatigue make the diet impossible to sustain.
  • Your metabolism adapts and progress stalls.

A good floor is roughly 1,500 calories for men and 1,200 for women — but honestly, slower and steadier almost always wins. Not sure where to start? See How Many Calories Should I Eat a Day?.

Step 4: Protect your muscle with protein

In a deficit, protein is your best friend — it preserves muscle and keeps you full. Aim for roughly 1.6–2.2g per kg of body weight. For the full breakdown of protein, carbs, and fat, read Understanding Macros.

Step 5: Track consistently — this is where most people fail

Here's the catch: a calorie deficit only works if you actually hit it, and you can only hit a target you can see. Studies repeatedly show people underestimate their intake by hundreds of calories. That untracked latte, that handful of trail mix, that splash of oil — they quietly erase your deficit.

This is exactly where tracking earns its keep. With Calorie AI, you just say what you ate and get an instant calorie estimate, so staying under your target becomes a habit instead of a chore. (More on why this matters in Why Calorie Tracking Matters.)

Adjust as you go

Your TDEE isn't fixed forever. As you lose weight, your body burns slightly fewer calories, so progress can slow. When you stall for 2–3 weeks, recalculate your maintenance with your new weight and trim another 100–200 calories — or add activity. Treat it as a feedback loop, not a one-time setup.

The takeaway

Calculating a calorie deficit is straightforward: find your TDEE, subtract 300–700 calories, prioritize protein, and track consistently. The math gets you the target — but consistency gets you the results. Make logging effortless and the deficit takes care of itself.

Hit your deficit without the spreadsheet

Knowing your target is step one. Hitting it every day is what counts. With Calorie AI, just say what you ate and watch your numbers add up automatically.

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The math is simple. We make the daily tracking simple too.