By Center for Personal Finance editors

Only 39% of investors between 21 and 50 years old are confident they have enough money for retirement. But most (63%) of this group have yet to develop a detailed financial plan for retirement, and many underestimate how long they will live in retirement, according to new research from T. Rowe Price, Baltimore.

Of the investors surveyed who have a detailed plan, 58% say they believe they will have enough money to retire, according to the survey, which focused on IRAs (individual retirement accounts) and the investing practices of Generation X (ages 35 to 50) and Generation Y (ages 21-34).

Sixty-three percent of investors age 50 and younger expect to receive Social Security benefits.

"This research underscores the fact that many more young investors need to get started planning for their retirement, even though the date may be decades away," says Christine Fahlund, senior financial planner at T. Rowe Price.

She noted the study also "demonstrates the important financial and psychological benefits of having a detailed savings and investment plan. Whether they do it on their own by using planning tools or by working with an adviser, the earlier investors begin saving, the more years their assets will be able to compound and potentially grow."

The survey looked at components a detailed plan might include. Of those who have a plan, 77% say it would target an anticipated monthly budget; 84% would have a specific monthly withdrawal strategy; and 78% would consider life expectancy and how long their savings might need to last.

Gen Xers and Yers say they expect to receive income from multiple sources. Most common are:

• 401(k)s or other workplace retirement plans (74%)
• IRAs (65%)
• Nonretirement accounts such as checking, savings, stocks, bonds, and mutual funds (64%)

Sixty-three percent of investors age 50 and younger expect to receive Social Security benefits. "Younger investors' confidence in the Social Security system was surprisingly positive," Fahlund says. "Still, it shouldn't be relied upon too heavily. Investors need to consider it as only one source of retirement income and make sure they are contributing to their retirement through other accounts."

Gen Xers and Yers expect to receive income from multiple sources.When asked at what age they expect to retire, the mean age given was 62. When asked how many years they expect to live in retirement, the mean answer was 22 years. The latter number is a significant underestimate, Fahlund notes.

"To be adequately prepared and to ensure they don't outlive their money, investors should save at least 15% of their salary, including any available employer match, and consider a possible retirement of 30 or more years, to age 95," Fahlund adds.

The online survey was conducted by Harris Interactive on behalf of T. Rowe Price among 860 adults between the ages of 21 and 50 who have at least one investment account.