Reuters There was a period, back in the late 1990s, when 401(k) plans were hailed as the key to every household's financial dreams. Put money in your 401(k), the thinking went, and you will retire a millionaire, thanks to the magic of the stock market, which would reliably deliver 15% annual returns.* A 401(k) plan is a defined contribution (DC) plan (other types include 403(b), 457, and SEP-IRA plans, as well as IRAs), meaning that participants put some of their income into the plan (along with, in some cases, additional money contributed by their employer); when they retire, they get that money back, along with any investment returns it has earned along the way.