Would your retirement savings be better in a Roth? Lots of investors would prefer to use tax-free Roths but can't because they earn too much to open an account. But for those who have settled for a traditional IRA , there's an option: convert it into a Roth to escape tax in retirement.

If this seems appealing, it's time to study up, as the steps have to be completed by Dec. 31 to qualify for the 2016 tax year.

It's not an easy decision because it entails paying a tax now to avoid one later.

"Every year I walk through the advantages of Roth conversions with at least 30 clients, and every year they all walk away with a clear understanding of the benefits and a commitment to make the move," says Gary Borowiec of Atlas Advisory Group's metro New York office. "Out of those 30, only five will actually write the check. No matter how much they get it intellectually, physically paying the taxes on that account is an emotional and financial hurdle many people just can't seem to overcome."

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But many experts say a conversion can be a good deal, not just because of ultimate tax savings but because a Roth can be passed to heirs tax-free, while passing on a traditional IRA can saddle heirs with a big tax bill. Also, unlike a traditional IRA, a Roth does not require minimum withdrawals after the investor turns 70 1/2. The tax-free compounding can just keep going. And if you earn income after that age, you can continue putting money in.

As mentioned, there's no free lunch . With a traditional IRA, the deal with Uncle Sam often allows a tax deduction on contributions, and tax deferral on investment gains until the money is taken out after age 59 1/2, when withdrawals are added to the investor's taxable income.

The Roth offers no deduction on contributions, but also no tax on gains or withdrawals.

To open a Roth the investor must have an annual income below $117,000 for singles or $184,000 for a married couple filing a joint return. Maximum contribution is $5,500 per year, $6,500 for an investor older than 50.

These requirements make Roths out of bounds for many investors. But anyone can convert a traditional IRA into a Roth regardless of income.

The catch is the converted amount is treated as ordinary income in the year the change is made. Not only does that mean paying tax on that money, the sum can lift the investor into a higher tax bracket. So it makes sense to do it when your income and tax bracket are low.

"Retirees may have a window to execute a conversion before they begin taking their Social Security and/or pensions while they are in a low tax bracket," says Maria L. Sciuto, a planner with Forté Capital in Rochester, New York. "Younger people with smaller IRA ... account balances may also be good candidates for Roth conversions if they are in a low tax bracket."

A conversion will pay off only if the Roth grows in value, she notes. Otherwise, you pay a big tax to convert to avoid a smaller tax you would have owed on the IRA.

Deciding whether to convert depends on a number of criteria, including expectations about future investment returns and inflation, and even life expectancy. Search for "Roth conversion calculator" for tools that can help.

But the most important is your best guess about the tax rate you would pay in the future versus your rate the year the conversion is done. If you think it will be higher, you could pay tax on the converted sum at today's lower rate to escape a higher tax rate later, and a conversion would make sense.

No one knows, of course, what Washington will do with tax rates years or decades down the road. Some experts think the huge national debt makes future increases all but inevitable.

Your future rate would also depend on your income, assuming Congress does not scrap the progressive income tax system. Retirement income will come from predictable sources like a pension and, assuming no radical changes, Social Security, and from sources that are harder to be sure of, like the size of your nest egg.

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Many investors assume their gross income will drop in retirement, but that's not necessarily the case for taxable income. People in middle age or older may find later that they have fewer federal-tax deductions for things like mortgage insurance, real estate taxes and dependents, keeping taxable income high. Some states, for instance, waive tax on pension and other retirement income, reducing the state tax deduction on the federal return. Income could go up if investments do very well, or a big inheritance arrives.

Still, many will indeed find their income and tax rate decline in retirement, making a Roth conversion a bad option.

"I think the biggest mistake people make is assuming the tax rate during retirement will be the same or higher," says Russell Holcombe of Holcombe Financial in Atlanta. "I think most retirees pay a much lower tax rate because they have no wages. Dividends and (long-term) capital gains tax rates (on investments) are much lower than ordinary income tax rates."

So it's worth sitting down to list the conditions that could cause your income and tax rate to go up.

If conclusions about your future tax rate make converting a close call, the decision may hinge on the other considerations like escaping required minimum distribution rules on the traditional IRA, or leaving assets to heirs tax free.

The bank, brokerage or mutual fund company that has your IRA can help you with the conversion.

For the conversion to pay off, the investor should have other money to pay the tax bill, so that the entire IRA can be moved into the Roth, Sciuto says. Otherwise, the Roth will start out so much smaller than the former IRA that you may never break even.

Investors who worry the conversion will saddle them with too much tax that year, or lift their bracket, can convert just part of the IRA to keep their income from ballooning. Some investors hold off until their IRA is in a slump, so the tax will be smaller and any rebound will be tax-free in the Roth. Leaving some money in a traditional IRA also can provide flexibility in the future, allowing tax-free Roth withdrawals in years other income and tax rate are high, and taxable IRA withdrawals when they are low.

"Investors should have their accountant project what tax bracket they are in and determine how much the investor can convert before hitting the next tax bracket," Sciuto says.

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So there's a lot of thinking to do if a conversion might be an option for you this year.

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