Calorie Deficit Guide: How to Lose Weight with TDEE & Macros

What Is a Calorie Deficit?

A calorie deficit occurs when you consume fewer calories than your body burns in a day. When this happens consistently, your body turns to stored fat for energy, resulting in fat loss over time. The basic math: a deficit of 3,500 calories over time equals approximately one pound of fat lost. A daily deficit of 500 calories produces about 1 lb/week of loss; 250 calories/day produces 0.5 lb/week.

Calculating Your TDEE (Total Daily Energy Expenditure)

TDEE is the total number of calories your body burns in a day, including your basal metabolic rate (BMR) plus all activity. It's calculated by multiplying your BMR by an activity multiplier:

Sedentary (desk job, little exercise): BMR × 1.2
Lightly active (light exercise 1–3 days/week): BMR × 1.375
Moderately active (moderate exercise 3–5 days/week): BMR × 1.55
Very active (hard exercise 6–7 days/week): BMR × 1.725
Extremely active (physical job + hard training): BMR × 1.9

Your TDEE is your "maintenance calories" — eating at this level, your weight stays the same. To lose weight, eat below TDEE. To gain muscle, eat above TDEE.

Setting a Safe Calorie Deficit

The optimal deficit for most people is 250–500 calories below TDEE per day. This produces 0.5–1 lb/week of weight loss, which is considered sustainable and preserves muscle mass.

Avoid going below these minimums, regardless of your deficit calculation:

Women: Never below 1,200 calories/day
Men: Never below 1,500 calories/day

Eating below these minimums causes muscle loss, nutrient deficiencies, metabolic adaptation ("starvation mode"), and is not sustainable. Aggressive deficits of 1,000+ cal/day are associated with rapid rebound weight gain.

Macros for Fat Loss

While total calories are the primary driver of weight loss, macronutrient distribution (macros) determines whether you lose fat or muscle:

Protein: 0.7–1.0g per lb of bodyweight. High protein is the most important macro for fat loss — it preserves muscle mass during a deficit, increases satiety, and has a higher thermic effect (burns more calories to digest). A 170 lb person should aim for 120–170g protein/day.
Fat: Minimum 0.3–0.4g per lb bodyweight. Fat is essential for hormones and absorption of fat-soluble vitamins. Don't drop dietary fat too low.
Carbohydrates: Fill remaining calories with carbs. Carbs fuel workouts and brain function. There's no need to go extremely low-carb unless you prefer that eating pattern.

Tracking Calories Effectively

The most effective way to maintain a calorie deficit is to track what you eat, at least initially. Apps like MyFitnessPal, Cronometer, or LoseIt make this manageable. Use a food scale (not measuring cups) for accuracy — a tablespoon of peanut butter measured by volume can vary by 50+ calories from the label. After 4–8 weeks of consistent tracking, most people develop enough intuition to maintain their deficit without measuring everything.

Dealing with Plateaus

Weight loss always slows over time as your body adapts. If you've been in a deficit for 8+ weeks and weight loss has stalled for 2+ weeks: recalculate your TDEE at your new lower bodyweight, take a brief "diet break" (1–2 weeks at maintenance calories), or add 30 minutes of exercise 3 days/week. Gradual, patient progress beats aggressive restriction every time for long-term results.

Frequently Asked Questions

How big of a calorie deficit should I be in?

A deficit of 250–500 calories per day is optimal for most people — producing 0.5–1 lb of weight loss per week while preserving muscle mass. Larger deficits (750–1,000/day) accelerate short-term weight loss but increase muscle loss, cause more fatigue, and are harder to sustain. Start with a 300–400 calorie deficit and adjust based on actual results after 2–3 weeks.

How many calories is 1 pound of fat?

One pound of pure fat contains approximately 3,500 calories. In practice, a 3,500-calorie deficit over time doesn't always translate to exactly 1 lb of fat loss due to water retention, muscle changes, and metabolic adaptation. The 3,500-calorie rule is useful as a rough guideline for planning, but actual results vary. Most people find a 500-calorie daily deficit produces slightly less than 1 lb/week in practice.

What happens if my calorie deficit is too large?

Deficits over 1,000 calories/day — or eating below 1,200 (women) or 1,500 (men) calories — trigger muscle loss as the body cannibalizes muscle for energy, dramatic reduction in metabolic rate, nutritional deficiencies, hormonal disruption (including thyroid and sex hormones), extreme fatigue, and a high likelihood of rapid weight regain when normal eating resumes. Slow and steady always wins for sustainable fat loss.

Should I count calories or macros?

Both are effective. Counting total calories is simpler and sufficient for weight management if you're eating a balanced diet. Tracking macros (protein, carbs, and fat grams) gives more control over body composition — particularly preserving muscle during fat loss by ensuring adequate protein intake. Most people find that hitting their protein target (0.7–1g/lb bodyweight) while staying in a calorie deficit produces the best results without needing to track every gram.

How do I calculate my maintenance calories?

Calculate your BMR using the Mifflin-St Jeor equation (widely considered the most accurate), then multiply by your activity factor to get TDEE. Example for a 35-year-old, 170 lb, 5'10" man: BMR = (10 × 77 kg) + (6.25 × 178 cm) − (5 × 35) + 5 = ~1,800 cal. Multiply by 1.375 (lightly active) = ~2,475 maintenance calories. For weight loss, target 2,000–2,200/day.