Calorie deficit: how to calculate it right to lose fat

What exactly is a calorie deficit

Your body burns a certain amount of energy each day (your TDEE, or total daily energy expenditure). If you eat fewer calories than that, your body taps its reserves — mainly fat — to cover the difference. That's a calorie deficit, and it's the physical basis of any fat loss.

It doesn't matter whether the diet is keto, intermittent fasting, paleo or flexible: they all work because, one way or another, they make you eat fewer calories than you burn. The deficit is the cause; the method is just the tool to get there.

Step 1: calculate your expenditure (TDEE)

First you need your basal metabolic rate (BMR) — the calories you burn at rest — multiplied by an activity factor. The Mifflin-St Jeor equation is the most reliable for the general population. Then the factor is applied based on how much you move and train.

Instead of doing the math by hand, the DietPlanner Pro calculator estimates your TDEE from your weight, height, age, sex, body-fat % and training frequency, and returns your target calories for cutting directly.

Step 2: subtract 15% to 25%

• •Moderate deficit (15–20%): the recommended option for most. Sustainable loss and better muscle retention.
• •Aggressive deficit (20–25%): useful if you have a lot of fat to lose or little time, but harder to maintain.
• •Rule of thumb: aim to lose 0.5%–1% of your body weight per week. Faster usually means more muscle loss.

Step 3: protect muscle while you lose fat

A deficit without strength training and without enough protein makes you lose a significant chunk of muscle along with the fat. Two non-negotiables: keep strength training, and raise protein to the high end, 1.8–2.2 g per kilo, especially in a deficit.

Protein is also the most satiating macro and the one that costs the most energy to digest, so it helps twice over: it preserves muscle and reduces hunger.

What to do when the scale stalls

Stalling is normal. As you lose weight your expenditure drops (a lighter body burns less), so the deficit you had is no longer one. Before cutting more, check the basics: are you measuring portions accurately? Have you unconsciously reduced your daily activity?

If the weight has been truly flat for 2–3 weeks, cut another 100–150 kcal or raise activity slightly. Don't slash calories all at once: the more room you leave yourself now, the more tools you'll have later.

Common mistakes

• •Overly aggressive deficits from day one: unsustainable and they leave you no room to maneuver.
• •Forgetting liquid calories, cooking oil and uncounted snacking.
• •Not adjusting calories as you lose weight.
• •Dropping strength training and doing only cardio: you slim down, but lose muscle and end up "skinny-fat".