Inflation, return on investments, desired retirement income, taxes -- they all play an important role in guaranteeing that cushy retirement you've planned. But perhaps the most important concern is, well, how long you live to enjoy the fruits of your labor and low-carb diet.

Retirement planning is so simple, says our own in-house retirement expert David Braze (TMF Pixy): "The only trick involved is to ensure you die on schedule." Morbid, we know. But entirely necessary, unless you want to get stuck performing savings CPR. To ensure you won't outlive your money, you need an idea of how long you're going to live. So put on a happy face and play... The Longevity Game!

Northwestern Mutual developed this "game" to estimate a life expectancy based on responses to various questions. While those number-crunching folks at insurance companies don't know when a particular individual may die, actuaries can use piles of historical data to estimate a life expectancy based on age, family history, and medical history.

If you watch how your responses affect your life expectancy, you can get an idea of what you can do to prolong that inevitable date. (For a second opinion, check out MSN's life expectancy calculator.)

Keep in mind that the result is the average life expectancy of people in the given circumstances. In other words, about half of the people in those circumstances lived longer than what the "age tabulator" indicates. So, when calculating how long you need your retirement kitty to last, tack on another 10 years or so to the result of the Longevity Game, just to be safe.