Calculating a calorie deficit involves determining how many fewer calories you consume compared to how many your body burns. First, find your Total Daily Energy Expenditure (TDEE) using an online calculator or formula that includes your Basal Metabolic Rate (BMR) and activity level. Then, subtract a desired number of calories to create a deficit, often around 500-1000 calories per day for weight loss. What are your fitness or health goals that you're planning around this calorie deficit?