Roth IRA Conversions Sound Smart - But These 5 Costly Moves Can Backfire

Paying taxes today to avoid them later sounds like a winning retirement strategy. That's the basic appeal of a Roth IRA conversion: move money from a traditional IRA into a Roth, pay income taxes now, and enjoy tax-free qualified withdrawals in retirement.

Done carefully, the strategy can work exactly as intended. The catch is that the taxable portion of the amount you convert is generally added to your income for that year, and that can trigger a series of unintended consequences for your retirement plan. Below are five costly financial mistakes that can turn a smart Roth IRA conversion into an expensive one.

Converting too much in a single year

One of the biggest mistakes is converting a large balance all at once. The taxable portion of a traditional IRA conversion generally counts as ordinary income in the year of the conversion. That extra income can push you into a higher federal tax bracket than you expected.

For example, someone near the top of the 22% bracket who converts a large IRA balance could suddenly find part of that conversion taxed at 24% or higher. The conversion itself may still make sense over the long term, but paying more tax than necessary reduces the strategy's benefit.

Some taxpayers choose to spread conversions across several years, particularly when they expect temporarily lower taxable income.

Accidentally triggering Medicare IRMAA surcharges

Higher taxable income can also affect your Medicare costs. Medicare Part B and Part D premiums are subject to Income-Related Monthly Adjustment Amounts (IRMAA). These surcharges are based on your modified adjusted gross income from two years earlier.

That creates what many retirees call a "cliff." Going just one dollar over an IRMAA threshold can move you into the next premium bracket, resulting in hundreds or even thousands of dollars in additional Medicare costs over the following year.

Because a Roth conversion increases taxable income, it can unexpectedly push retirees over one of those thresholds. If you are already close to an IRMAA threshold, keeping the conversion below the next bracket could prevent a disproportionate increase in Medicare premiums.

Causing more of your Social Security to become taxable

Many retirees overlook another consequence of higher income. The IRS determines how much of your Social Security benefits is taxable using what's known as combined income, which includes adjusted gross income, tax-exempt interest, and half of your Social Security benefits.

A Roth conversion increases adjusted gross income, which can cause a larger share of Social Security benefits to become taxable. Up to 85% of Social Security benefits can be included in taxable income once combined income exceeds certain thresholds.

Although the conversion may still make sense over the long run, triggering additional taxes on Social Security benefits can make the immediate cost much higher than expected.

Paying the conversion tax from your IRA

Another common mistake is using retirement savings to pay the tax bill. Ideally, the taxes owed on a Roth conversion should come from money outside the retirement account. Doing so allows the entire converted amount to remain invested inside the Roth, where future qualified growth and withdrawals can be tax-free.

Using part of the IRA to cover the tax reduces the amount transferred into the Roth and therefore the amount available for future tax-free growth. If you are younger than 59 1/2, the portion withheld or distributed rather than converted may also be subject to the 10% additional tax unless an exception applies.

Ignoring your future income picture

Many people focus only on today's tax rate without considering where they may be in a few years. Relatively low-income periods can offer favorable opportunities for Roth conversions, such as the years between retirement and claiming Social Security or before required minimum distributions begin.

Those years may offer an opportunity to convert smaller amounts while remaining in a relatively low tax bracket. By contrast, waiting until required minimum distributions, pensions, and Social Security are all generating taxable income can make Roth conversions much more expensive.

Rather than asking whether to convert, many retirement planners recommend asking how much to convert each year without triggering unnecessary taxes or surcharges.

Why smaller conversions can work better

Instead of converting an entire IRA in one year, many retirees spread the process over several years. Converting smaller amounts allows taxpayers to "fill up" their current tax bracket without spilling into the next one. It may also help avoid crossing Medicare IRMAA thresholds or increasing the taxable portion of Social Security benefits.

The strategy requires more planning, but it may reduce the total tax cost compared with making one large conversion, particularly when it helps avoid higher tax brackets and income-related surcharges. Every retirement situation is different, and the optimal amount depends on current income, expected future tax rates, retirement timing, and other sources of income.

Bottom line

Roth IRA conversions can be an effective way to reduce taxes later in retirement, but the size and timing of the conversion matter just as much as the decision itself.

Converting too much in one year can trigger a higher tax bracket, increase Medicare premiums, and make more of your Social Security benefits taxable. Before converting a large balance, it's worth calculating not only the income tax you'll owe this year, but also how the extra income could affect the rest of your retirement plan if you are hoping to retire comfortably.

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