It's the question that haunts you as you approach retirement age: What's my "retirement number"?  The number represents how much you'll need in the bank before you can retire without having to worry about running out of money.

Though there's no surefire way to know with 100% certainty what this number needs to be, there are a dizzying array of variables to take into consideration that can make the process seem impossible.

But there is hope where many see despair.

The slideshow below takes the average American household -- a 50-something couple with take-home pay of about $50,000 after taxes -- and shows how many of the assumptions financial experts think you should make can overstate your retirement number by over 40%.

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