Overestimating the market, a lack of understanding their retirement needs, and simply failing to plan led to some boomers being so woefully unprepared. According to the survey, when boomers started saving they expected their investments to grow by 8.7 percent each year. In reality, compound annual growth rate of the S&P 500 from 1958 through 2008 was 6.6 percent. Surveyed boomers said they plan on spending about 10 percent of their savings every year of their expected 21-year retirement, although experts recommend withdrawing no more than 4 percent. And, despite over two-thirds of boomer who say their retirement expectations have changed in the past year, nearly the same percent have no formal plan.