MANY PEOPLE DREAM of retiring early, but few actually make it a reality.

Taking certain proactive measures, such as investing in a 401(k) in your 20s and eliminating debt, will help set you on the path to early retirement. But even if you achieve these goals, it's nearly impossible to know whether that nest egg will be enough to get by. (Click here to help you figure out how long your retirement savings will last.) You'll have to consider certain factors such as the lifestyle you'd like to maintain, the number of years before you start receiving Social Security checks (full benefits generally kick in sometime between age 65 and 67, depending on the year you were born) and the unanticipated but costly health expenses that could pop up along the way.