For average investors who are overwhelmed by financial choices and have little time or energy to devote to retirement planning, target date mutual funds, which automatically shift to a more conservative mix of stocks and bonds as investors get older, are an attractive option.

"It's a conservative way to approach retirement funding," said Nadav Baum, managing director of investments at BPU Investment Group, Downtown. "I don't use them. It really depends on the client and how much volatility [he] can accept."

Also known as life cycle funds and age-based funds, target date funds let investors determine the year they want to retire and as the years go by rebalance to more heavily weighted with bonds and less invested in stocks as the retirement date nears.

"It used to be by the time it hit the target date, the fund was close to 100 percent bonds, but retirement planners realized people are living longer in retirement," said Steve Dimitriou, managing partner at Mayflower Advisors in Boston.

"So, over the last few years, the allocation has changed to reflect more of a life planning strategy," he said. "I like the idea of 'set it and forget it.' It works. … The costs are high to truly diversify, and target date funds make it more possible."

Target date mutual funds are not without their disadvantages.

They typically have a fee in addition to the existing fees of the mutual funds that the target date fund invests in, which adds to the overall expense of the investment. Also, they are inflexible and often do not take into account changes in the global economy.

Few target date funds will have exposure to growth economies, such as China, India, the Middle East and Latin America.

"I don't really see an advantage to them," said Bruce Fenton, president of Atlantic Financial in Boston, a firm that specializes in global investing. "Target date funds are harmful in the sense that you are paying extra fees with very little advantage."

With target date funds, the fund's name often includes the retirement year. They are usually spaced five years apart: 2010, 2015, 2020, etc.

But critics of target date funds wonder how one fund can really suit the needs of everyone who is planning to retire in a given year.

"As advisers we don't like target date funds generally because they impose an asset allocation on clients that might not be appropriate based on their needs, circumstances and objectives," said Bob Jazwinski, president of JFS Wealth Advisors in Hermitage and chairman of the personal financial specialist committee of the American Institute of Certified Public Accountants.

There are now 43 mutual fund companies offering target date funds, which have combined assets of $187.66 billion, according to Morningstar Inc. The funds have gotten a boost in recent years from the federal pension bill, which made target date funds the default investment option for more 401(k) retirement plans.

Stacy Francis, president of Francis Financial in New York, calls target date funds the "little black dress" of the investment world because they can be right for so many different people with different needs and occasions.

"It's an investment that will stand the test of time and make the grunt work of investing even easier," Ms. Francis said. "A lot of people in America don't have a financial adviser to call so they have to be their own adviser.

"For them, target date funds are great. But if someone is working with an adviser, there are other funds that might better suit their needs."

Manning & Napier Advisors in Rochester, N.Y., was among the early pioneers of life cycle funds in the 1980s, said Craig Abbott, vice president.

He said a lot of the growth in life cycle funds could be traced back to the bear market of 2002 when many people doing their own investing lost a lot of their hard-earned money, which really highlighted the need for professional money management.

"There's a range of mistakes people made," he said. "Not being diversified enough, chasing returns and bailing out of falling funds. Investing is tough, especially when things get rocky."

The combination of stock, bonds and cash in a target date fund can give many investors a good night's sleep knowing their portfolio is self-balancing. Even investors with aggressive target date funds will know their portfolio has lower risk compared with other funds because of the rebalancing effect.

"People are looking for something that makes sense and doesn't take a lot of their time," said Jerome Clark, portfolio manager of retirement funds for T. Rowe Price in Baltimore. "Studies have shown about 80 percent of investors are hands-off investors."

Mr. Clark said that because the retirement of tomorrow will be very different than retirement today, more attention needs to be paid to what target date funds do 30 to 40 years after retirement.

"Inflation is the 800-pound gorilla in the room. It's the enemy of your asset," he said. "People have to consider [stocks] throughout their lifetime."

Some advisers says target date funds have allowed average Americans to benefit from a service that in the past could be afforded by only wealthy investors. (Before computer modeling, all of this work was done by hand, so only the rich could afford to hire advisers to do it).

The automation of a target date fund can free up advisers to do other things for their clients such as reviewing insurance, estate and college plans, said Luis Muniz, a district manager at First Command Financial Services in Carlisle.

"This is what advisers should be doing," he said. "Not worrying about alphas, betas and asset allocation. Many advisers are afraid to use target date funds. The average broker needs to prove his worth by doing asset allocation.

"The true planner worries about so many things that [target date funds] are the perfect vehicle for them. It frees them up to handle everything else."