NEW YORK (TheStreet) -- The biggest retirement mistakes have nothing to do with investing, says Ed Slott, founder of Ed Slott & Company.

"Not maximizing retirement contributions is a major error that a lot of people make," Slott says. "People need to take advantage of every option to keep putting money away in a retirement account."

Slott tells folks aged 50 and older not to miss catch-up contributions so as not to lose out on opportunities to save for retirement. He adds that future retirees should take advantage of spousal IRAs for nonworking spouses and tells them to keep making Roth IRA contributions even after 70½ if they have the earnings.

Another big no-no in Slott's opinion: retiring too early.

"The longer you work and keep earning, the more retirement money you can continue to sock away in a Roth IRA," says Slott. "If you are still working, you can probably avoid taking Social Security for longer, allowing your future benefit to increase substantially. From age 62 to age 70, your monthly check goes up every month you delay."

You must begin IRA distributions by April 1 of the year after the year you turn age 70½ or face a 50% penalty for missing a required minimum distribution. And when it comes to RMDs, Slott reminds his clients not to make calculation errors by using the wrong table and to make sure they use the right accounts.

He also suggests that employees know all six of their options when leaving a job: (1) IRA rollover; (2) keeping the funds in the plan; (3) rolling the funds into a new company's plan; (4) taking a lump-sum distribution; (5) converting the funds to a Roth IRA; and (6) converting the funds to a company plan Roth 401(k).

Lastly, Slott says that retirees can't forget about tax efficiency just because they stopped working full time and are no longer pocketing a steady paycheck.

"It's a mistake not to leverage the tax code," says Slott. "Failing to do a Roth conversion and not using the Roth recharacterization strategy is silly. It's not how much you convert, it's how much you recharacterize."

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