The Ultimate Retirement-Planning Riddle: How Much Do I Need to Save?

The most common question people ask when it comes to retirement is: "How much do I need to save?" Unfortunately, there isn't an easy answer, or even a very accurate calculation or rule of thumb to rely on.

But that doesn't mean you should take a stab in the dark. For most people, the best answer is to save "as much as you can," says Timothy Maurer, a certified financial planner and author of The Financial Crossroads.

"What I really think it comes down to is cash flow. You can find the most complex retirement calculator, and even it may fall short of giving you an accurate answer because it doesn't take into account what we haven't seen in life – not just in the stock market, but also the way that our lives tend to be volatile, and we go through stretches where someone loses a job. So save what you can, when you can," he says.

I think that's good advice, but I also think it helps to have a ballpark, something to shoot for so you don't slack off. That's typically a percentage of your income, and it's a bit of a moving target. When you're flush, you save more. When money is tight – as it may be now – you may have to dial back your efforts a bit. Maurer calls this the barbell scenario.

"There are different phases in life when you have a greater ability to save, so you need to be flexible. When people get married, and they have a double income with no kids, I encourage them to save in excess of 20% of their income. Once they start having kids, their income may shrink, and expenses will increase, so their ability to save drops tremendously. As soon as the kids graduate from college, they may be able to get back up to that 20% savings rate."

The years you save more will balance out the years you save less, and over the long haul, you should aim for an average of 15% of your income. Other tips:

* Envision what retirement means to you. If you're thinking vacations and spoiling the grandkids, you're going to need to save more than someone who plans to continue working, at least part-time, well past age 65. You really need to sit down and think about your goals: When you want to retire and what you want that retirement to look like. If you get to your target age and you don't have enough, you'll need to make adjustments by working a bit longer or dialing back your lifestyle a bit.

* Consider Social Security. It helps to estimate how much money you can expect from Social Security, and to do that, you can use the calculator at www.ssa.gov. Be sure to choose the option that allows you to see your monthly benefit in inflated dollars.

* Run some numbers. I know that retirement calculators rely on estimates and assumptions, but I also know that I like to see things in black and white. If you're like me, consider filling out the Ballpark E$timate worksheet from the American Savings Education Council and the Employee Benefit Research Institute. It's the best tool I've seen, and you can find it here.

* Practice. When retirement is looming – say three to five years away – take a detailed analysis of what you anticipate your retirement expenses to be, and then practice living on that. "Often, at this point people are making substantially more than they need to live off of, because these are the peak earning years. So I recommend people live off what they'll have in retirement as sort of a test drive," says Maurer. Not only will you learn to live on a fixed income, but you can bank the rest.