Evaluating Longevity Calculators

Want to feel like a god? Go online and use a life-expectancy calculator. Your answers to health, family history, and lifestyle questions can either add or subtract lots of years from your life--all at the click of your mouse.

The calculators are not authoritative and don't claim to be, particularly for those with serious pre-existing medical conditions. However, they're indicative of where your life is headed, at least in terms of longevity. That's important because nearly every investment and retirement expert emphasizes that most people greatly underestimate how long they will live. As a result, their retirement plans--which are already modest for starters--fall woefully short of providing them retirement income for the rest of their lives.

I test-drove a handful of calculators and most of them produced comparable results. They do ask different questions, so, as with other tests, I'd suggest tossing out the top and bottom results and using the numbers that pop up most frequently. The most important benefit of these calculators is not the projected life span they indicate, but the often-dramatic impacts that lifestyle choices can have on longevity.

Here's an example: Northwestern Mutual's Lifespan Calculator is easy to use and has just been updated to reflect new life-expectancy data. That's crucial because lifespans are getting longer, so calculators based on older longevity data tend to produce inaccurately low results. The calculator asks 15 questions. The only factors you can't control are your current age, gender, height, and family health history. Here are the other question areas and the length (in years) of the longevity impact of the "best" and "worst" lifestyle choices: blood pressure (six years), stress (two), exercise (six), diet (five), seatbelt use (six), driving (13), drinking (seven), smoking (10), drugs (nine), and doctor visits (two). The factors and their impacts on longevity are based on data from the National Center for Health Statistics, a company spokeswoman says.

I took the test three times. Here are the results:

1. The "truth." Honest and accurate answers to all questions. I will live until age 96 (note to sons: sorry, boys. Your inheritances will be slightly delayed.
2. Worst-case answers. I smoke, take drugs, eat poorly, live on a couch, and so on. I will live until age 55. The calculator actually took a good number of years off my current age, even though I entered that age to start the exercise!
3. Best-case answers. I live at the gym, subsist on vegetables and free-range nuts, and have no stress, When you look in Guinness World Records under healthiest human beings, it shows my picture. I will live until age 100. (The new mortality tables include lifespans of up to 121 years.)

Based on research studies, Northwestern Mutual says, you control 70 percent of your health and longevity variables, and your genetic make-up controls only 30 percent. Here are other calculators to check out: Microsoft, Living to 100 (its developer was profiled in a 2007 U.S. News story), Peter Russell and MetLife.