TDEE for Weight Loss — How Big Should Your Calorie Deficit Be?

Everyone who's tried to lose weight has heard some version of "eat less, move more." That's technically correct but not very useful. The real question is: how much less? And the answer depends on your TDEE — your total daily energy expenditure.

Calculate your TDEE using the TDEE Calculator before picking a deficit. The calculator estimates how many calories you burn per day based on your age, weight, height, and activity level. Once you have that number, the deficit math is straightforward.

What a Calorie Deficit Actually Means

A calorie deficit means you're consuming fewer calories than your body burns. The shortfall has to come from somewhere, and over time it comes mostly from stored fat (with some muscle loss mixed in, which is why protein intake and resistance training matter).

The rough standard: a deficit of 3,500 kcal per week equates to approximately 0.45 kg (1 lb) of fat loss. That's 500 kcal/day below maintenance. In practice, the number isn't perfectly linear — hormones, water retention, and metabolic adaptation complicate the math — but the 500 kcal/day ≈ 0.5 kg/week relationship is a reasonable planning estimate.

Your TDEE is your maintenance level. If your TDEE is 2,400 kcal/day and you eat 1,900 kcal/day, you're in a 500 kcal deficit. If you eat 2,100 kcal/day, you're in a 300 kcal deficit. Both produce fat loss; just at different speeds.

How to Set Your Deficit Based on Your Goal

The right deficit size depends on how fast you want to lose weight, how much you have to lose, and how much disruption you're willing to accept in energy, training, and daily life.

Moderate deficit: 300–500 kcal/day below TDEE

Rate of loss: ~0.3–0.5 kg (0.6–1 lb) per week

This is the most practical range for the majority of people. It produces meaningful fat loss without the fatigue, hunger, and performance impact that comes from aggressive restriction.

At a 400 kcal deficit, a person with a TDEE of 2,400 kcal eats 2,000 kcal/day. That's enough food to train, recover, maintain reasonable energy, and sustain the deficit for months without grinding down.

The moderate deficit is also the best choice for preserving muscle mass. Aggressive deficits increase muscle breakdown, particularly when protein is insufficient. At 300–500 kcal below maintenance with adequate protein (1.6–2.2g per kg of body weight), most fat loss comes from fat stores rather than muscle.

Aggressive deficit: 500–750 kcal/day below TDEE

Rate of loss: ~0.5–0.75 kg (1–1.5 lb) per week

Appropriate for people with a significant amount of fat to lose (generally 25%+ body fat), where faster initial progress makes sense and the body has ample fat stores to draw from.

At higher body fat percentages, the body is more willing to mobilize fat stores and less likely to cannibalize muscle. A 600 kcal deficit that would leave a lean person feeling depleted may be well-tolerated by someone with substantial body fat reserves.

The tradeoff is sustainability. Aggressive deficits are harder to maintain past 8–12 weeks, often produce more fatigue, and require careful protein management to minimize muscle loss.

Large deficit: 750–1,000 kcal/day below TDEE

Rate of loss: ~0.75–1 kg (1.5–2 lb) per week

This territory is appropriate only in specific circumstances: medically supervised weight loss, preparation for bariatric surgery, or individuals with obesity-related health conditions where rapid weight loss has clear medical benefit.

For most people, deficits above 750 kcal/day produce disproportionate muscle loss, significant fatigue, hormonal disruption (particularly in women), and are very difficult to sustain. The faster loss on the scale often includes a larger proportion of muscle and water than a more moderate approach.

A general rule: don't eat below 1,200 kcal/day for women or 1,500 kcal/day for men, regardless of what the deficit math suggests. Below these floors, it's extremely difficult to meet micronutrient needs, and the physiological cost increases steeply.

Very small deficit: 100–300 kcal/day below TDEE

Rate of loss: ~0.1–0.3 kg per week

Sometimes called a "mini cut" or "slow cut." Appropriate for people who are already lean (12–17% body fat for men, 20–25% for women) and want to reduce body fat without sacrificing training performance or muscle mass.

At low body fat percentages, aggressive deficits cause measurable strength and muscle loss quickly. A 200–250 kcal deficit that produces slow, steady fat loss over 12–16 weeks often preserves more muscle than a 600 kcal deficit over 6 weeks, even if total fat lost is similar.

Calculating Your Deficit: A Worked Example

Person: 35-year-old man, 85 kg, 178 cm, moderately active (desk job, trains 4× per week)

Step 1: Calculate BMR using Mifflin-St Jeor BMR = (10 × 85) + (6.25 × 178) − (5 × 35) + 5 BMR = 850 + 1,112.5 − 175 + 5 = 1,792.5 kcal

Step 2: Apply activity multiplier Moderately active = BMR × 1.55 TDEE = 1,792.5 × 1.55 = 2,778 kcal

The TDEE Calculator does this automatically — enter your stats and it returns the result immediately.

Step 3: Set target intake by goal

For this person, 2,278 kcal/day is a reasonable moderate cut — still enough food to train well, plenty of room for protein targets (at 1.8g/kg, that's 153g of protein, leaving ~1,500 kcal for fats and carbs).

Why TDEE-Based Deficits Are More Accurate Than Generic Advice

Generic calorie targets — "eat 1,500 calories to lose weight" — ignore the fact that TDEE varies enormously between individuals. A sedentary 50-year-old woman at 58 kg might have a TDEE of 1,750 kcal. A 25-year-old man who trains daily might have a TDEE of 3,200 kcal. A 1,500-calorie diet is a 250 kcal deficit for the first person and a 1,700 kcal deficit for the second.

The second person eating 1,500 kcal would lose weight extremely fast in the short term, experience significant muscle loss and fatigue, and likely rebound once the diet ends. The first person might lose slowly at 1,500 kcal and would be better served by a different target.

Your TDEE is your personal maintenance level. The deficit calculation starts there, not from a generic number.

Protein, Macros, and Deficit Quality

A calorie deficit is necessary for fat loss, but the composition of those calories affects how much of the loss comes from fat versus muscle.

At a minimum, aim for 1.6g of protein per kg of body weight while in a deficit. Some research supports going higher (up to 2.4g/kg) for lean individuals or those doing heavy resistance training. At 85 kg, that's 136–200g of protein per day.

Higher protein during a deficit:

• Preserves more muscle mass (the primary benefit)
• Increases satiety per calorie consumed
• Has a slightly higher thermic effect — more of those calories are burned in digestion

The Macros Calculator can help you set protein, fat, and carbohydrate targets once you've established your calorie goal from TDEE.

Metabolic Adaptation: Why Your TDEE Changes During a Diet

TDEE isn't fixed. As you lose weight, your body burns fewer calories — a smaller body requires less energy for everything from moving around to maintaining organ function. A person who starts at 95 kg with a TDEE of 2,900 kcal will have a lower TDEE at 80 kg, even at the same activity level.

On top of this, caloric restriction triggers metabolic adaptation — the body reduces energy expenditure beyond what the weight loss alone would predict. This is why weight loss stalls after a few months even when nothing in the diet appears to have changed.

The practical response: recalculate your TDEE every 3–4 weeks as your weight changes, and adjust your intake accordingly. What was a 500 kcal deficit at 95 kg may only be a 300 kcal deficit at 88 kg — requiring you to either reduce intake further or increase activity to maintain the same rate of loss.

Diet breaks — short periods at maintenance calories, typically 1–2 weeks — can partially restore TDEE and reduce the psychological burden of extended restriction. The research on this is mixed, but many practitioners find that planned breaks improve long-term adherence without significantly derailing progress.