Millions of business owners may be underprepared for retirement, according to a new survey that shows small business owners do not have a clear picture on how much money they'll need when they retire.

According to The American College, the Bryn Mawr, Pa.-based educational institution devoted to financial services, roughly a third of the women and a quarter of the men surveyed say they've not estimated what they will need financially when they retire.

Additional findings from the research raise questions about the quality of retirement preparation being done by the majority of small business owners. For example, while 66 percent of the women and 70 percent of the men said they had developed an estimate of their retirement needs, only half of these individuals have done so with the assistance of a financial professional.

According to the survey, an estimated 25 percent of the participants used online calculators, which often have serious limitations in adequately projecting changes in inflation, taxes, medical expenses and income streams. The remainder of those queried arrived at an estimate by performing simple calculations themselves using pencil and paper.

Probably the most distressing survey finding is that even among those small business owners who have calculated their retirement goals, most haven't laid out a formal plan to achieve their financial objectives. Among the small business owners surveyed, 77 percent of the women and 74 percent of the men have no written plan for retirement.