The fundamental mechanism of weight loss is well-established: consume fewer calories than your body expends over time, and body fat is used to make up the difference. The math is simple. The execution is harder. But it starts with knowing your numbers.

Step 1: Find Your TDEE

Your Total Daily Energy Expenditure (TDEE) is how many calories you burn per day at your current activity level. It is calculated from your Basal Metabolic Rate (BMR) — the calories burned at complete rest — multiplied by an activity factor.

The Mifflin-St Jeor equation for BMR (most accurate for most people):

• Men: (10 x weight in kg) + (6.25 x height in cm) – (5 x age) + 5
• Women: (10 x weight in kg) + (6.25 x height in cm) – (5 x age) – 161

Activity multipliers: sedentary (x1.2), lightly active (x1.375), moderately active (x1.55), very active (x1.725).

Step 2: Set Your Deficit

One pound of fat contains approximately 3,500 calories. To lose one pound per week, you need a 500-calorie daily deficit (500 x 7 = 3,500).

• 0.5 lb/week: 250 calorie/day deficit — sustainable long-term
• 1 lb/week: 500 calorie/day deficit — the standard recommendation
• 1.5 lb/week: 750 calorie/day deficit — aggressive but manageable
• 2 lb/week: 1,000 calorie/day deficit — maximum sustainable for most people

Below 1,200 calories/day (women) or 1,500 (men) without medical supervision risks nutrient deficiencies, muscle loss, metabolic adaptation, and hormonal disruption.

Why Faster Is Not Better

Aggressive deficits (1,000+ cal/day) trigger metabolic adaptation — your body downregulates TDEE by reducing activity, lowering body temperature, and slowing non-exercise movement. The result: you plateau faster, feel worse, and are more likely to regain weight after. A moderate deficit of 400-600 calories/day produces more sustainable results in most research.

Protein Intake During a Deficit

Eating adequate protein during a calorie deficit is critical for preserving muscle mass. Target 0.7-1.0 grams per pound of lean body mass. Higher protein intake also increases satiety, meaning you feel fuller on fewer calories.

Tracking Methods That Work

You do not have to count every calorie forever. But tracking for 2-4 weeks builds awareness of where your calories actually come from — which is usually more surprising than expected. Apps like Cronometer or MyFitnessPal with a food scale for the first few weeks calibrates your intuition for the long term.