To estimate your daily calorie needs to lose weight: 1. Calculate your basal metabolic rate (BMR) using the Harris-Benedict formula, which takes into account your height, weight, age, and sex. 2. Determine your activity level and multiply your BMR by a corresponding percentage: sedentary (20%), lightly active (30%), moderately active (40%), very active (50%), or extra active (60%). 3. Add the activity number to your BMR. Eat fewer calories than this total each day to lose weight, re-calculating as your weight changes. Most people can lose weight eating around 1,500 calories daily.