One of the primary goals of retirement planning is to figure out how to use your retirement assets in the best way to generate the income you'll need after you stop working. But to do this, it is important to have a pretty good idea as to the amount of income you'll actually need. Estimating this is not a simple matter because there are so many things to consider. How much income will you need to pay your bills and essential living expenses? What amount do you want to spend for travel, pursuing hobbies and living your retirement dreams? How might your needs for income change over time as you age? What rate of inflation should you assume in your planning? These and other factors mean that the exact amount of income you'll want to try to plan for is not static. Instead, it's fluid and ever-changing. Therefore, establishing accurate future income targets is a complex, but necessary component to sound retirement income planning. A good financial advisor will typically spend hours, with the help of sophisticated computer programs to narrow all of this down to realistic lifetime income objectives. Once this is done, the planning job shifts to figuring out the best way to marshal all retirement assets so that they can produce this required income.   But there are many so-called professionals out there who will tell you that it's easy to cut through all this clutter and complexity by instead using a simple retirement rule of thumb. The advice is… "You'll need 70 to 80 percent of the income you made in your final years of employment in order to live a comfortable retirement."  Well, that's easy enough.  Or is it?