First, the good news. Studies have shown that retirees and near retirees are actually quite good predictors of their own expected remaining years of life (see, for example, "Perception of Mortality Risk: Implications for Annuities" by Drinkwater and Sondergeld). Further evidence of this is provided by the life insurance industry, which has found that people purchasing annuities (who derive maximum benefit only if they live for a long time) actually live longer than what standard mortality tables would predict.
The bad news, however, is that the chance you will outlive your savings, and suffer a sharp drop in your standard of living (known as "longevity" or "mortality" risk) usually gets less attention from retirees than concerns about their health and their investment returns. As a starting point, you can download standard mortality tables that predict both individual and joint life expectancy, based on your current age (our tables come from the U.S. Internal Revenue Service, the national tax authority). Life Expectancy Table.
Unfortunately, the tables only show the "most likely" remaining life expectancy; in practice, there many outcomes on either side of this estimate. Given this, there is no way to escape the need to make a trade-off. On the one hand, you can assume a short remaining life expectancy. This minimizes the chances of leaving accidental bequests that are larger than you intended. However, it also raises the risk of you outliving your savings, and eventually falling below your target income and desired standard of living. On the other hand, you can assume a very long life expectancy. While this reduces the chances of outliving your savings, it also raises the chances that you will leave a larger than intended bequest.
One possible solution to this dilemma is the conversion of part of your savings into an annuity. Should You Annuitize?.