How Many Calories Should You Eat to Lose Fat?

The internet will give you a hundred different answers to this question. Most of them are wrong, oversimplified, or trying to sell you something. Here's what the research actually says.

Step 1: Calculate your maintenance calories

Your Total Daily Energy Expenditure (TDEE) is the number of calories your body burns in a day — including your basal metabolic rate, the thermic effect of food, and your physical activity. Eat at your TDEE and your weight stays stable. Eat below it and you lose weight. That's thermodynamics.

The most validated equation for estimating BMR is the Mifflin-St Jeor equation, published in 1990. Multiple validation studies have confirmed it's the most accurate predictive equation for the general population, outperforming the older Harris-Benedict equation.

You then multiply your BMR by an activity factor to get your TDEE. Sedentary (×1.2), lightly active (×1.375), moderately active (×1.55), very active (×1.725), or extremely active (×1.9).

Reference: Mifflin, M.D. et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 51(2), 241-247.

Step 2: Set your deficit

A calorie deficit is what drives fat loss. But how large should it be?

Research consistently shows that a moderate deficit of 20–25% below TDEE produces optimal results for most people. This is aggressive enough to produce meaningful fat loss (0.5–1% of body weight per week) but conservative enough to preserve muscle mass — especially when combined with resistance training and adequate protein.

Larger deficits (30%+) accelerate weight loss on the scale but carry trade-offs: greater muscle loss, increased hunger and cravings, hormonal disruption, and a higher likelihood of regaining the weight. The research on metabolic adaptation shows that extreme deficits trigger disproportionate drops in energy expenditure.

Reference: Helms, E.R. et al. (2014). Evidence-based recommendations for natural bodybuilding contest preparation. Journal of the International Society of Sports Nutrition, 11, 20.

Step 3: Prioritise protein

During a calorie deficit, protein becomes more important, not less. Higher protein intakes protect lean mass during weight loss and improve satiety — both critical for long-term adherence.

The current evidence supports 1.8–2.7g of protein per kg of body weight during a fat loss phase. The higher end of this range matters more when deficits are larger or when you're leaner.

For an 80kg person, that's 144–216g of protein per day. This is higher than the standard recommendation (0.8g/kg) because the standard recommendation is designed to prevent deficiency, not to optimise body composition during a deficit.

Reference: Helms, E.R. et al. (2014). A systematic review of dietary protein during caloric restriction in resistance trained lean athletes. International Journal of Sport Nutrition and Exercise Metabolism, 24(2), 127-138.

Step 4: Track and adjust

Every equation is an estimate. Individual variance of 10–15% is normal. Two people with identical stats can have meaningfully different metabolic rates due to genetics, NEAT (non-exercise activity thermogenesis), gut microbiome, and other factors.

The equation gives you a starting point. Real data gives you the answer. Track your weight daily, calculate weekly averages, and adjust after 2–3 weeks if the trend isn't moving in the right direction.

• Losing too fast (more than 1% body weight per week): increase calories by 100–200 kcal
• Not losing: reduce by 100–200 kcal or increase activity
• Losing at 0.5–1% per week: you're in the sweet spot — change nothing

Common mistakes

Cutting too aggressively

A 1,200 calorie diet is not a strategy. It's a countdown to a binge. Moderate deficits are sustainable. Extreme deficits are temporary.

Ignoring protein

You can be in a perfect calorie deficit and still lose muscle if protein is too low. The deficit drives fat loss. Protein protects muscle. You need both.

Overcomplicating it

Meal timing, carb cycling, and supplement stacks are noise. Energy balance and protein are the signal. Get those right first. Everything else is a rounding error.

The bottom line

Calculate your TDEE. Subtract 20%. Eat 1.8–2.7g protein per kg. Track for 2–3 weeks. Adjust based on real data. That's it. No meal plan. No supplements. No secrets. Just math, protein, and patience.