Many of us are still living in the past when it comes to planning for retirement.  Sure, we know that unlike previous generations we can't rely on generous Social Security benefits or fat corporate pensions.  And we know that we can't count on double-digit market returns to make up the difference.

But as a recent Fidelity survey shows, we're not all that confident that we (or our parents) will be able to retire in the style to which we've become accustomed — if we are able to retire at all.

Some interesting statistics from the Fidelity survey:
Four in 10 Americans are somewhat or very concerned about their parents' preparedness for retirement.  What mistakes did they say their parents made?

• Started saving too late
• Didn't save regularly
• Underestimated health-care costs
• Didn't get help and advice

The truth is that the lifestyle you can afford in retirement largely depends on you.  How diligently you save.  How wisely you navigate today's challenging markets.  And, most importantly, how realistic you are in the assumptions you make about your retirement planning.

Your best bet before you go ahead and start putting the numbers into a retirement calculator is to answer some really key questions about those assumptions and the life you hope to live.

Do you need $1 million to retire comfortably?
No.  Sure, it would be nice to accumulate seven figures, but for most of us that goal is unreasonable and unnecessary.  The fact is, most Americans can call it quits with assets well below $1 million.  And if you don't build up as much as you'd hoped, there are a variety of moves you can make to compensate.

NBC NEWS SPECIAL SERIES A series airing all week on Today, Nightly News, CNBC and MSNBC reports on what you need to know about retirement planning. Interactive map: Where are the seniors? Vote: Are you ready for retirement? Study: Most retirees regret poor planning Interactive: How much will you need to retire? Interactive: Net worth calculator Retirement series: ‘Start Thinking Now’

For example, if your home has increased in value, you may be able to downsize to smaller digs (or move to a cheaper locale) and come away with a tidy profit.  If you're not interested in moving on and moving out, you can still convert your home's equity into tax-free monthly income by taking out a reverse mortgage.

Will retirement living cost as little as I anticipate?
Not necessarily.  The rule of thumb here is that you can comfortably live on 70 to 80 percent of your pre-retirement income because taxes and job-related expenses (commuting, work clothes) drop once you leave the work force.  But rules of thumb are made to be broken, and while that 70 to 80 percent works on average, there may be a lot of reasons why it wouldn't work for you. 

For example, if you're planning on paying off your mortgage and paying for your children's college before you retire, you're probably in good shape.  But if you've refinanced your mortgage and will have to continue paying after you stop working, that might be a problem.  And if you're planning to travel to all the places you couldn't see while you were chained to your desk, you may end up spending even more.  The key is to plan a budget for your retirement life.  Researchers have found that people who take the time to do this are more likely to be come up with an accurate assessment and less likely to err on the downside. 

So, if you're within 10 years of retirement, estimate your future expenses as best you can — vanguard.com has a good worksheet in its retirement planning section.  If retirement is more than a decade away, figure you'll need at least 90 percent of your pre-retirement income.  If that means you end up with more than you need, you can always decide to live larger.

They say historically the market has returned between 10 and 11 percent.  Can I expect to earn that much on my investments?
Nope.  Anticipate 6 to 8 percent instead.  We all got a little spoiled in the '80s and '90s.  As they say on TV, past results are not indicative of future performance.  Given that stock prices compared to earnings are still a little lofty right now, you're better off betting on 8 or 9 percent for stocks and 5 to 6 percent on bonds, for a diversified portfolio of 6 to 8 percent a year.  Clearly, lower returns mean you'll have to sock away more cash to meet your goals.

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