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Do you plan on working to 65 or perhaps even later?

If so, it would be well worth coming up with a backup plan.

While 70% of people plan to work until 65, less than 30% actually do, according to Michael Conrath, chief retirement strategist for JPMorgan Asset Management. In fact, most retire by 62.

"It's a big gap," Conrath said in a recent episode of Decoding Retirement (see video above or listen below). "It just shows people have plans, and then life comes at them and things change."

Sometimes, people make retirement decisions that are entirely within their control, Conrath said.

But that's not always the case. Your company may downsize, or you may experience a health problem or disability. Sometimes, you become a caregiver. There could be any number of reasons, according to JPMorgan's Guide to Retirement.

"What people have in mind years before retirement may not be where they land," he said. "So you've got a plan for those what-if situations."

Read more: Here's what to do with your retirement savings in a market sell-off

At the same time, a significant number of workers will stay on the job. More than 27% of those ages 65 to 74 are still in the workforce, and even among those 75 and older, over 8% remain employed.

"Retirement is no longer this binary decision to work or to retire," Conrath said.

That shift is clearly visible in the data. Using anonymized information from Chase banking customers, Conrath noted that the firm found that 53% of households are partially retired. These individuals are drawing from sources like Social Security, pensions, or annuities while still earning some wage income.

"There’s this hybrid approach," Conrath said, and it comes with nuances.

Some people continue working simply because they enjoy it. "They love what they're doing," he said. "They love the social elements ... they have a purpose."

But others remain in the workforce out of necessity. According to Conrath, partially retired households tend to carry more debt and spend more, which influences their retirement timing. As a result, this group often transitions to full retirement later than those who retire all at once.

"They're working to be able to maintain that spending but also pay off their debt," he said.

A key part of planning is preparing for a time horizon that could span 35 years or more, partly due to living longer but also because you may retire sooner than expected.