Target-date fund assets exploded to $485 billion as of Dec. 31, according to Morningstar Inc. That was up 579% since 2005, the year before their popularity began to soar.

The Pension Protection Act in 2006 OK’d their use as default investments for people who are automatically enrolled in their workplace’s 401(k) plan.

They’re also popular among people who don’t want to make their own buy and sell decisions.

U.S. diversified stock fund assets rose only 10.9% in the same period.

Target-date funds are the one-stop-shopping version of mutual funds.

All you have to do is make three decisions.

• 1. Pick a fund whose target date matches your retirement date.

• 2. Make sure that fund has the level of volatility you’re comfortable with as it travels to its target date.

• 3. Get a handle on whether the fund stops tweaking its portfolio at the target date. Many continue to pare their growth stocks and boost their bond holdings for years afterward.

That’s it. The fund manager does the rest. He picks an initial asset mix that is appropriate for your age and risk tolerance. Then he typically fine-tunes that asset mix as you age, as you approach retirement and as your desire for stability of principal grows.

Some funds aim for more growth along the way, which can make their annual gains and losses more dramatic bumpier.

Others sacrifice growth to give you a smoother ride.

Whatever style you choose, the fund manager makes all the changes as years go by. That spares you from having to pick the right mix of stocks, bonds and funds, changing that mix over and over as you age.

Some target-date funds are better for you than others. Investment strategies can differ, even among funds with the same target date.

And do not confuse target-date funds with lifestyle funds. Those sometimes called asset allocations funds start with an asset mix that is growth oriented or more cautious. Unlike target date funds, lifestyle funds don’t change their orientation. If one starts out geared for growth, that’s how it stays. If you use a lifestyle fund, you can shift by switching to increasingly conservative lifestyle funds.

Don’t overlook additional investment options for your portfolio.

Many employers, consultants and regulators think target-date funds failed to live up to their hype during the financial crisis of 2008-09, says a McKinsey & Co. study. They did not shield shareholders enough from the market downturn. The most growth-oriented target-date funds with a 2050 or later target averaged a 3.73% annual gain over the five years ended March 21.