If you're wondering how long you'll live, try this

How long will you live? If you knew for sure, it would be a lot easier to plan how long your retirement savings needs to last. Knowing how many years you have left means you could more easily determine how fast you could draw down your retirement savings, select appropriate investment strategies and decide whether it's a good idea to delay Social Security or buy an annuity.

But one of life's little realities is that you could live for a long time -- or not very long at all. You just don't know.

Still, you can take some steps to help figure out your future. Here's one that's easy and fun. A new online tool at the website Flowingdata helps you see for yourself the different possibilities that could occur with your life.

All you do is input your current age and gender, and you'll see your possible future life spans play out in a fascinating animated chart. In some, you live a long time, and sometimes not long at all. But frequently, it's somewhere between these two extremes.

Flowingdata's tool uses mortality data from the Social Security Administration that reflects the experience of all working Americans. Most likely, you'll see a better outcome than the tool shows if you've completed college, earn above-average income or don't smoke. But even with those conditions, the picture is still basically the same: a wide range of possible future outcomes.

Because of this uncertainty, it's a good idea to develop reliable sources of retirement income that will last for the rest of your life, no matter how long you live. Such sources include Social Security, a traditional pension if you have one and a simple payout annuity from an insurance company (which acts like a personal pension).

Consider these sources as insurance against the possibility that you might live a long time.

This possibility was recently and vividly illustrated by the experience of one of our neighbors, whose 97-year-old aunt moved in with them because she ran out of money, lamenting that she hadn't expected to live so long.

When people anticipate a potentially short future lifespan, some will justify shortsighted decisions, like retiring early, starting Social Security as soon as possible and spending their savings rapidly. "Enjoy it while you can, because you just never know" is their typical line of thinking.

They dismiss strategies to protect themselves against the possibility of living a long time, such as delaying Social Security benefits or spending down savings conservatively. They think, "I'd be mad if I died after delaying my Social Security benefits, or if I kicked the bucket before spending all my money."

Actually, you wouldn't be mad -- you'd be dead, and we really don't know if you can really be mad in that case. But because you can most likely imagine being alive, old and poor -- like our neighbor's aunt -- it simply makes sense to plan for all possibilities.

When you see potentially short future lifespans using Flowingdata's tool, use that as motivation to make important life decisions that don't inspire short-sighted decisions about money. Tell children, friends and relatives how much you care for them, and do something special for them.

Take care of unfinished business, such as making up with friends or relatives you may be estranged from, or visit long-lost relatives. Take up that hobby or cause you've always wanted to pursue, or find ways to travel without busting the bank.

Live for today -- and tomorrow. Because you never know if you might live a long, long time.