The third number you need to know is your weight. Dr. Oz says to weigh yourself at least once a week. "The reason for that is you can slip a long way in a month, as we learned over the holidays," he says.

Dr. Oz urges people to think of weighing themselves as a GPS, not punishment. "The GPS is going to say, 'At the next available moment, make an authorized U-turn.' You made a mistake. It's okay," he says. "Make a turn and go back. Otherwise, you get mad at yourself."