How many calories should I eat in a deficit?

Calculate your TDEE (BMR × activity factor) and subtract 250–500 kcal for a sustainable deficit. A 500 kcal/day deficit targets ~1 lb/week loss. Never go below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.

How fast should I lose weight on a calorie deficit?

0.5–1% of bodyweight per week is the commonly recommended rate for preserving muscle. For an 80 kg person, that's 0.4–0.8 kg/week. Faster loss (1–2 lbs/week) is feasible but increases muscle loss risk, especially as you get leaner.

Why did I stop losing weight despite being in a calorie deficit?

Metabolic adaptation. Your body reduces TDEE in response to sustained restriction — less NEAT, lower thyroid output, reduced leptin. Solutions: recalculate macros based on current weight, take a 1–2 week diet break at maintenance, or increase activity to restore the deficit.

Does a calorie deficit cause muscle loss?

A deficit alone doesn't cause muscle loss, but inadequate protein and no resistance training do. Keep protein at 1.8–2.4 g/kg bodyweight and continue strength training. Research consistently shows that high protein + resistance training preserves lean mass even in significant caloric deficits.

What is the difference between calorie deficit and intermittent fasting?

Intermittent fasting (IF) is an eating pattern that restricts the window when you eat — it doesn't automatically create a calorie deficit. Most IF research shows benefits are due to reduced calorie intake enabled by the eating window restriction, not the fasting itself. Both approaches can work; the best one is the one you'll adhere to.

Calorie Deficit Calculator: How to Create a Safe Deficit for Fat Loss

Calculate your ideal calorie deficit for sustainable fat loss. Covers how to find TDEE, why a 500 kcal/day deficit targets 1 lb/week, and how to avoid muscle loss.

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The Calorie Deficit Principle

Fat loss requires a calorie deficit — consuming fewer calories than your body burns. One pound of fat contains approximately 3,500 kcal. A sustained 500 kcal/day deficit theoretically produces 1 lb of weight loss per week.

Calories in − Calories out = Energy balance - Negative balance → weight loss - Zero → maintenance - Positive → weight gain

In practice, the 3,500 kcal/lb rule is an approximation — metabolic adaptation, water retention, and changes in lean mass affect actual results.

Step 1: Calculate TDEE (Your Calorie Out)

TDEE = BMR × Activity Factor

Mifflin-St Jeor BMR (most accurate widely-used formula): - Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5 - Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161

Activity factors: 1.2 (sedentary) → 1.375 (light) → 1.55 (moderate) → 1.725 (active) → 1.9 (very active)

Example: 35-year-old male, 80 kg, 178 cm, moderately active: - BMR = (10 × 80) + (6.25 × 178) − (5 × 35) + 5 = 800 + 1,112 − 175 + 5 = 1,742 - TDEE = 1,742 × 1.55 = 2,700 kcal/day

Step 2: Set Your Deficit Size

Deficit	Weekly Loss Target	Best For
250 kcal/day	~0.5 lb/week	Preserving muscle; slow and steady
500 kcal/day	~1 lb/week	Standard; sustainable for most people
750 kcal/day	~1.5 lb/week	Faster loss; monitor muscle retention
1,000 kcal/day	~2 lbs/week	Maximum — generally the upper safe limit

Absolute minimum calorie floors: - Men: Not below 1,500 kcal/day - Women: Not below 1,200 kcal/day

Going below these thresholds causes significant muscle loss, hormonal disruption, and micronutrient deficiencies.

Metabolic Adaptation: Why Deficits Get Harder Over Time

The body adapts to prolonged calorie restriction through adaptive thermogenesis — involuntary reductions in TDEE:

Non-exercise activity thermogenesis (NEAT) decreases: you fidget less, move less
Thyroid hormones (T3/T4) decrease, slowing metabolism
Leptin (satiety hormone) drops, increasing hunger

After 8–12 weeks of deficit, TDEE may decrease by 5–15%. This is why weight loss plateaus despite maintained deficit. Solutions:

Diet breaks: 1–2 weeks at maintenance calories to restore hormones
Refeed days: 1 day/week at maintenance
Recalculate TDEE based on new body weight (you burn fewer calories at lower weight)
Increase activity to expand the calorie gap

Protein's Role in Preserving Muscle During a Deficit

High protein intake is the most important factor in preserving lean mass during fat loss:

Protein Intake	Muscle Loss Risk During Deficit
1.0 g/kg	High — typical of low-protein diets
1.6 g/kg	Moderate — adequate for sedentary individuals
2.0–2.4 g/kg	Low — recommended for athletes and strength trainers

Research shows that protein intakes of 2.0–2.4 g/kg during calorie restriction preserve significantly more lean mass than lower intakes, even at identical calorie deficits.

Rate of Loss by Starting Body Fat %

Higher body fat % allows a larger deficit with less muscle loss risk:

Body Fat %	Recommended Max Deficit
> 30%	Up to 1,000 kcal/day
20–30%	500–750 kcal/day
15–20%	300–500 kcal/day
10–15% (lean)	200–300 kcal/day
< 10% (very lean)	100–200 kcal/day

Lean individuals have less fat to mobilize — the body is more likely to catabolize muscle when fat stores are limited.

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Frequently Asked Questions

How many calories should I eat in a deficit?: Calculate your TDEE (BMR × activity factor) and subtract 250–500 kcal for a sustainable deficit. A 500 kcal/day deficit targets ~1 lb/week loss. Never go below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.
How fast should I lose weight on a calorie deficit?: 0.5–1% of bodyweight per week is the commonly recommended rate for preserving muscle. For an 80 kg person, that's 0.4–0.8 kg/week. Faster loss (1–2 lbs/week) is feasible but increases muscle loss risk, especially as you get leaner.
Why did I stop losing weight despite being in a calorie deficit?: Metabolic adaptation. Your body reduces TDEE in response to sustained restriction — less NEAT, lower thyroid output, reduced leptin. Solutions: recalculate macros based on current weight, take a 1–2 week diet break at maintenance, or increase activity to restore the deficit.
Does a calorie deficit cause muscle loss?: A deficit alone doesn't cause muscle loss, but inadequate protein and no resistance training do. Keep protein at 1.8–2.4 g/kg bodyweight and continue strength training. Research consistently shows that high protein + resistance training preserves lean mass even in significant caloric deficits.
What is the difference between calorie deficit and intermittent fasting?: Intermittent fasting (IF) is an eating pattern that restricts the window when you eat — it doesn't automatically create a calorie deficit. Most IF research shows benefits are due to reduced calorie intake enabled by the eating window restriction, not the fasting itself. Both approaches can work; the best one is the one you'll adhere to.

Last updated 7/28/2026