Americans fear running out of money in retirement more than declining health. That worry is justified, as longevity is the greatest threat to a secure retirement, says Pamela Yellen, a financial-security expert.

“Over the last 40 years, there has been a dramatic shift away from company pension plans that promised workers a certain amount of money every month in retirement for as long as they lived,” Yellen said. “Instead, there’s been a shift toward do-it-yourself, cross-your-fingers, hope-and-pray retirement planning strategies like 401(k)s and IRAs.”

Because people don’t know how long they’ll live or how much they can safely withdraw each year, they run the risk of spending too much too quickly and outliving your savings, or spending too conservatively and not being able to fully enjoy your retirement years, Yellen contends. “Traditional retirement investing strategies also make it virtually impossible to ensure a major market crash doesn’t cut the value of your savings in half when you might not have time to recover from it,” she added.

The Center for Retirement Research at Boston College and other experts recommend having an annuity to ensure your money lasts as long as you do. “Including the right kind of annuity in your financial plan takes the guesswork out of taking income in retirement and can free you from the fear and worry that most people live with,” said Yellen, whose books include “Rescue Your Retirement: Five Wealth-Killing Traps of 401(k)s, IRAs and Roth Plans — and How to Avoid Them.”