No one knows the future, but that shouldn't keep you from investing. Just keep your assumptions modest and presume, for example, that stocks will return about 5% a year for the next 20 years not 11%. Ditto for your home's value. Plan on 3% growth, not the historical rate of about 6%. That way you'll force yourself to save more aggressively and have a good chance of being pleasantly surprised years from now. What do these lower assumptions mean for your planning? Look at it this way: the typical retirement portfolio fell about 30% from top to bottom in the Great Recession. All else being equal, that loss requires a 43% portfolio gain to be made whole. With average annual returns of 5%, it would take 7.3 years to get even; with average annual gains of 11%, it would take less than half that long just 3.4 years. That means if you plan for 5% returns but get 11% returns, you'll either reach your goal twice as fast or end up with twice as much over the full period. That's sweet. By the way, there is a decent chance that historical rates of return will persist. Looking at rolling 30-year periods since the Great Depression, the S&P 500 index of large-cap stocks has never produced less than an average annual gain of 9%, and in almost every instance the average annual gain was between 10% and 12%. Yes, things are different now. We're in the throes of a slow economy with dismal returns, and that's why you need to scale back your assumptions. But at some point this too shall pass and rates of return will rise possibly enough to live up to those long-term averages.