Despite the way securities traditionally are sold and what you hear in the media, the stock market confoundingly defies prediction. Look at the two quarters ended March 30th, 2019: The 19.8% plunge in the Standard & Poor's 500 index in the fourth quarter of 2018 was a flash bear market; in the first quarter of 2019, a recovery was just as swift, a snapback gain of 13% gain. If whipsaw emotional shifts from fear to greed make it harder to stay realistic about what to expect from a prudently-designed retirement portfolio, this chart offers a way to know what to expect based on historical data.

This chart shows the returns of four asset classes as well as a portfolio invested in a mix of the four. The returns are based on the average annual return of each asset in the 93 years from 1926 through 2018. Of the four assets, the best performing were large-company stocks, as measured by the Standard & Poor's 500 index, which averaged a total return of 9.9% annually over the 93 years.

Each group of bars shows how often the four asset classes and the diversified portfolio achieved or bettered the long-term return of that particular asset class — 9.9% for large-cap US stock, 11.08% for small-cap US stock, 5.24% for US bonds, 3.39% for US cash, and 9.23% for a 4-asset portfolio — over rolling periods of five years versus 10, 15, 20, and 35 years.