“If a 30 percent drop in the stock market would cause a loss in a portfolio that the investor knows they cannot stomach, they have too much exposure to stocks,” said Doug Bellfy, a financial planner in South Glastonbury, Conn. “But this test is valid, regardless of where the experts think the market is at any given time or guess it will be in the near future — and it is a guess.”

Consider how much risk your plans require

Responsible financial advisers have a mantra: Don’t take on more risk than is necessary to reach your goals, whether it is the amount of money you think you need for retirement or for your child’s tuition.

“For many who have invested wisely over the last 10 year bull market, they no longer need to be heavily invested in stocks,” said James Sweeney, a financial planner in Lehi, Utah. “Their portfolio has grown to the point that they can reduce the risk and still meet their retirement goals.”

That might mean slightly scaling back the slice of a portfolio allocated to stocks based on individual circumstances. The percentage will not be the same for everyone, and it is a delicate balance: You do not, for example, want to become invested too conservatively as you approach retirement; your portfolio might need to last three decades or more. That means you will need enough stocks to help your money grow and keep pace with inflation.

Move to cash as needed

If you have an imminent need for cash but your money is tied up in stocks, now might be a good time to shift into something conservative, particularly if the need is likely to arise in five years or less. If you expect to buy a home in that time, you will need all that money at once. If you are paying a tuition bill, you will probably only need a quarter of your savings a year over four years.

“The more concentrated the outflow, the more important it is not to have your money at risk to satisfy near-term goals,” Mr. Bellfy said.

Retirees and people on the cusp of retirement have the most to lose if the markets come tumbling down. In such circumstances, keeping a year’s worth of basic living expenses in cash may be helpful as a long-term strategy. It can keep retirees from locking in losses by having to sell investments when they are down.