Weight Loss Calculator

The Science of Weight Loss

Weight loss fundamentally comes down to a calorie deficit: burning more calories than you consume. One pound of fat contains approximately 3,500 calories. To lose 1 pound per week, you need a sustained deficit of 500 calories per day. To lose 2 pounds per week, you need a 1,000 calorie daily deficit. This math is the foundation of every evidence-based weight loss approach.

However, the body is adaptive. As you lose weight, your metabolism slows — a smaller body burns fewer calories. This is why weight loss often stalls even when maintaining the same deficit. The adjustment is called metabolic adaptation, and accounting for it means recalculating your calorie target as you lose weight, approximately every 10 pounds.

How Your TDEE Is Calculated

This calculator uses the Mifflin-St Jeor equation — the most validated BMR formula for non-athlete adults — then multiplies by your activity factor to get your Total Daily Energy Expenditure (TDEE).

Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5

Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

TDEE = BMR × Activity Factor (1.2 to 1.9). Your calorie target = TDEE − daily deficit. The calculator will show your target and projected timeline to your goal weight.

Safe Rate of Weight Loss

The CDC and major health organizations recommend losing no more than 1–2 pounds per week for sustainable results. Faster loss typically involves significant muscle loss, nutrient deficiencies, and rapid regain when normal eating resumes. Here's what each rate means in practice:

• 0.5 lb/week: 250 cal/day deficit — mild, very sustainable, minimal hunger, preserves muscle well
• 1 lb/week: 500 cal/day deficit — the gold standard for most people, manageable and effective
• 1.5 lb/week: 750 cal/day deficit — aggressive but achievable, more hunger, requires discipline
• 2 lb/week: 1,000 cal/day deficit — maximum recommended; below ~1,200 cal for women or ~1,500 for men risks malnutrition

Macros for Weight Loss

Calories are the foundation, but macro composition matters for satiety and muscle preservation:

• Protein: 0.7–1g per pound of body weight. Protein is the most satiating macronutrient and critical for preserving muscle during a deficit. High protein intake consistently outperforms lower-protein diets for weight loss.
• Fat: Minimum 0.35g per pound (hormonal health). Don't go below 20% of total calories from fat.
• Carbohydrates: Fill the remaining calories. Low-carb and moderate-carb diets produce similar fat loss when protein and calories are matched — choose based on preference and adherence.

For a 200 lb person at 1,800 cal/day: aim for ~140g protein (560 cal), ~60g fat (540 cal), ~175g carbs (700 cal). This macro split maximizes satiety and muscle retention during the cut.

Why Weight Loss Stalls (Plateaus)

The dreaded plateau is real and physiological — not a character flaw. Three main mechanisms cause it:

• Adaptive thermogenesis: The body downregulates NEAT (non-exercise activity thermogenesis — fidgeting, posture, movement) by 100–400 cal/day in response to a deficit
• Reduced calorie cost of movement: A lighter body burns fewer calories doing the same exercise
• Calorie estimation errors: Studies show people underreport food intake by 20–50% on average

When you plateau, options include: re-weighing and logging food more precisely, adding 30 minutes of walking (burns ~150 cal), taking a 1–2 week diet break at maintenance (resets some adaptive thermogenesis), or accepting the plateau as a normal phase and staying consistent.

Exercise and Weight Loss

Exercise is valuable for health, fitness, and maintaining lost weight — but its direct calorie-burning contribution to weight loss is often overestimated. A 45-minute moderate-intensity gym session burns about 300–400 calories for a 180 lb person, which is just one slice of pizza. The primary driver of fat loss is dietary restriction, not exercise volume.

That said, resistance training is particularly important during a cut. It's the primary signal your body uses to preserve muscle rather than burning it for energy. Losing weight without lifting typically results in losing 25–40% of the weight as muscle. Losing weight while lifting preserves far more lean tissue, producing better body composition even at the same scale weight.

Frequently Asked Questions

Is 1,200 calories too low? For most adults, yes. 1,200 cal/day is the commonly cited minimum, but this came from 1970s studies on obese patients under medical supervision. For most active adults, staying above 1,400–1,600 cal for women and 1,600–1,800 cal for men maintains energy, adherence, and muscle better. Use the smallest deficit that produces acceptable weight loss speed.

Do I need to track calories? Not necessarily — but it's the most reliable method. If you don't track, focus on protein targets (use a food scale for protein sources), eliminate liquid calories, and use volume eating (high-satiety, low-calorie foods like vegetables) to manage hunger. Most successful long-term losers do track, at least initially.

How do I maintain weight loss? Maintenance requires continued vigilance — the body fights to regain lost weight for years. Strategies that work: consistent weigh-ins (weekly minimum), maintaining high protein intake, regular exercise (resistance + cardio), keeping calorie awareness even without active tracking, and having a plan for when weight creeps back.