The Basics of Weight Loss

Calculate your activity level. For a week or so, keep an activity journal and use a calorie calculator to figure out how many calories you burn while sitting, standing, exercising, lifting weights, etc. throughout the day. Another, easier option is to wear a heart rate monitor that calculates calories burned. After a week, add your totals for each day and average them out to get a general idea of how many calories you burn each day.

Keep track of how many calories you eat. For at least a week, enter and track your calories online (e.g., with Calorie Count) or use a food journal to write down what you eat and drink each day. Be as accurate as possible, measuring when you need to or looking up nutritional information for restaurants, if you eat out. After a week, add your totals for each day and average them out to get a general idea of how many calories you eat each day.

Add it up. Take your BMR number and add your activity calories. Then subtract your food calories from that total. If you're eating more than your BMR + your activity calories, you're at risk for gaining weight.