Calorie Deficit Calculator

Calculate the exact calorie deficit needed to reach your goal weight. Choose from mild, moderate, or aggressive deficit plans — each showing your daily target, weekly fat loss, and a personalised timeline.

Free No signup required Instant results Evidence-based formula

What Is a Calorie Deficit and How Does It Work?

A calorie deficit is the gap between how many calories you eat and how many your body burns. When you consistently eat less than your Total Daily Energy Expenditure (TDEE), your body must find energy elsewhere — and it turns to stored body fat.

One kilogram of body fat contains roughly 7,700 kcal of stored energy. A daily deficit of 500 kcal means 3,500 kcal of deficit per week — about half a kilogram of fat loss. It sounds simple because it is, at the macro level. The challenge is in the execution.

How to Choose the Right Deficit Size

The "right" deficit depends on your starting point, training volume, and how much time you have:

Close to goal weight (5–10 kg to lose): Use a mild deficit (−250 kcal). You have less fat to burn and more muscle to protect.
Moderate fat loss phase (10–25 kg): A moderate deficit (−500 kcal) with high protein is the gold standard.
Significant fat loss needed (>25 kg): An aggressive deficit (−750 kcal) can accelerate progress but should be cycled with 1–2 week diet breaks every 6–8 weeks to manage hormonal adaptations.

Athletes and heavy lifters should generally stay at mild-to-moderate deficits to fuel performance and muscle protein synthesis. Sedentary individuals without training goals can tolerate larger deficits.

Protecting Muscle While in a Deficit

The biggest risk of aggressive dieting is losing muscle alongside fat — a process called lean tissue catabolism. Three strategies significantly reduce this risk:

High protein intake: Aim for 1.8–2.2 g of protein per kg of body weight. This is the single most evidence-backed strategy for muscle preservation during a cut.
Resistance training: Lifting weights signals your body to keep muscle even when calories are low. Aim for 3–4 sessions per week targeting major muscle groups.
Moderate deficit: Very aggressive deficits (greater than 1,000 kcal/day) dramatically increase muscle loss rates regardless of protein intake.

Why Deficits Shrink Over Time

As you lose weight, your TDEE decreases — you're carrying less mass, which requires less energy to move. A deficit that produced 0.5 kg/week loss at 90 kg will produce less loss at 75 kg using the same calorie target.

This is why recalculating every 4–6 weeks (or after every 3–5 kg of loss) is essential. If fat loss stalls for 3 consecutive weeks, reduce calories by 100–150 kcal rather than making large cuts that impair training and recovery.

Refeed Days and Diet Breaks

Extended calorie deficits cause hormonal adaptations — leptin drops, cortisol rises, and metabolic rate can decrease by 10–15% beyond what weight loss alone predicts (adaptive thermogenesis). Planned refeed days (eating at TDEE for 1–2 days) and diet breaks (1–2 weeks at maintenance every 6–8 weeks) help manage these adaptations, improve adherence, and make long diets more sustainable.

Frequently Asked Questions

What is a calorie deficit?

A calorie deficit occurs when you eat fewer calories than your body burns in a day (your TDEE). The energy gap forces your body to draw on stored fat for fuel, resulting in fat loss. A deficit of 7,700 kcal is roughly equivalent to losing 1 kg of fat.

How large should my calorie deficit be?

For most people, a deficit of 300–500 kcal/day (moderate) is the sweet spot: large enough to produce consistent fat loss (0.3–0.5 kg/week) while preserving muscle mass and energy levels. Aggressive deficits above 750 kcal/day can be used short-term but increase the risk of muscle loss, fatigue, and metabolic adaptation.

What is the difference between mild, moderate, and aggressive deficits?

Mild (−250 kcal/day) produces slow, sustainable loss of about 0.25 kg/week — ideal for those close to their goal or doing heavy training. Moderate (−500 kcal/day) produces ~0.5 kg/week — suitable for most fat-loss phases. Aggressive (−750 kcal/day) produces ~0.75 kg/week — appropriate for those with significant fat to lose, but should be cycled with diet breaks.

Will I lose muscle on a calorie deficit?

Some muscle loss is possible on any calorie deficit, but you can minimise it by eating sufficient protein (1.8–2.2 g/kg of body weight), doing resistance training at least 3 days per week, and keeping the deficit moderate. Aggressive deficits with low protein and no strength training cause the most muscle loss.

How long will it take to reach my goal weight?

The calculator estimates your timeline based on the deficit you choose and the total weight you want to lose. Real-world progress is rarely linear — expect plateaus, and recalculate every 4–6 weeks as your TDEE changes with your new body weight.

Should I eat back calories burned from exercise?

This depends on how your activity level is set. If you selected an activity level that includes your workouts, your TDEE already accounts for them — don't add calories back. If you chose "sedentary" and plan to exercise separately, you may eat back 50–75% of estimated exercise calories to avoid too large a deficit.

What is the minimum safe daily calorie intake?

Most guidelines set minimums at 1,200 kcal/day for women and 1,500 kcal/day for men. Below these levels it becomes very difficult to meet nutritional needs, and the risk of muscle loss, fatigue, and nutrient deficiencies increases. This calculator automatically floors results at 1,200 kcal.

How do I calculate my calorie deficit without a calculator?

First calculate your TDEE using the Mifflin-St Jeor formula: (10 × kg) + (6.25 × cm) − (5 × age) + 5 (men) or − 161 (women), then multiply by your activity factor (1.2–1.9). Subtract your chosen deficit (250, 500, or 750) from that TDEE to get your daily calorie target.