The Biggest Mistakes Women Make When...Dieting

The rationale: "When I was in college, I dropped 10 pounds in two weeks by living on fat-free yogurt and running 5 miles every day."

The mistake: "When you drastically cut calories, you're telling your body to lower your metabolism and slow down weight loss," says Scritchfield. The problem is that your appetite may not easily adjust to your new restricted eating plan. So even if you drop pounds in the short term, you risk gaining them back—plus extra—as soon as you give in to satisfying your cravings.

Try this: While 2,000 calories per day is the average target for most Americans, this calculator or this tool can help you find the bull's-eye for your age, weight and activity level.