With retirement, there's really no such thing as normal.

Only 37 percent of U.S. workers retire from a full-time job and stay retired, according to a recent study, focused on people in their mid-50s through age 71, by the Rand Corporation, a nonprofit research organization.

Meanwhile, about 14 percent of people "retire" to a part-time job. Another 17 percent quit their full-time job and retire, only to return to the workforce some time later, according to the study, which was based on data on 2,920 people who were surveyed over 14 years.

About 26 percent of people continue to work, either full time or part time, past age 70, the study found.

"In the U.S., nontraditional paths are very common," said Peter Hudomiet, an associate economist at the Rand Corporation and co-author of the report.

Rick Kahler, a certified financial planner in Rapid City, S.D., isn't surprised.

"I've had clients quit and go back in two years," Kahler says. "Ultimately, a person that goes back probably didn't visualize or think through fully what retirement would be like."

In other cases, a significant life event — such as a spouse's death — or financial difficulties might play a part in people returning to the workforce.

The study also looked at whether our personalities might affect our retirement decisions. A clear link was found between being extroverted and staying in the workforce longer, in a part-time job, even after controlling for other factors.

"We saw that extroverts were more likely to work longer, but only in part-time jobs," Hudomiet says.

Of course, many different factors go into determining how and when we retire. Here are some steps you can take to determine your retirement timeline:

Check up on your savings. Finances are a huge factor in how and when you will retire. See if you are on track with a retirement calculator.

Know what you want. Before you retire, figure out your goals and plans. "Actually write out what you will be doing," Kahler said. "What would a normal day, a normal week, a normal month look like? This forces someone to actually put pen to paper as to how a day looks."

Talk with your spouse. It sounds obvious, perhaps, that you would talk about retirement with your partner. But Kahler said one of the biggest hurdles for couples is when one spouse is suddenly home all the time. Talk together about how life is going to look when one or both of you is retired.

Consider backup plans. You might plan to work full time until age 70, but what if you change your mind down the road, or your health deteriorates to the extent that you can't work anymore? One idea is to trim expenses now so you can hike your savings rate and improve your retirement outlook. Other potential backup plans include moving to a less-expensive locale in retirement, taking out a reverse mortgage, or figuring out other ways to cut costs or boost income, such as taking in a roommate.

Prepare for major change. Retirement is "a big deal," Kahler says. "Some people are really ready and handle it fine, but most people find the adjustment a little more daunting than they imagined," he says. "We tell people: Start preparing two or three years before."

Andrea Coombes is a writer at NerdWallet. E-mail: acoombes@nerdwallet.com. Twitter: @andreacoombes.