The Hidden Costs of a Roth Conversion: What to Consider Before You Convert

Roth conversions can have consequences that go well beyond the tax on the amount you convert.

A large conversion can increase taxable income and potentially affect your marginal tax bracket, Medicare premiums, Social Security taxation, or eligibility for certain tax benefits and subsidies. And if you don't have outside cash available to cover the tax, using part of the converted funds can reduce the amount that remains invested.

Tax planning is rarely about looking at one transaction in isolation. The better question is how the decision fits into your entire financial picture.

What Is a Roth Conversion?

A Roth conversion moves money from a pre-tax retirement account, such as a traditional IRA or a pre-tax 401(k), into a Roth IRA. You pay ordinary income tax on the pre-tax amount you convert in the year of the conversion. In exchange, qualified withdrawals from the Roth IRA are tax-free in the future, and Roth IRAs are not subject to required minimum distributions (RMDs) during the original owner's lifetime.

For many people, that trade-off can be valuable. But because the converted amount is added to your income for the year, the effects can ripple through other parts of your tax return and financial life.

How a Roth Conversion Can Push You Into a Higher Tax Bracket

The United States uses a progressive tax system, so each additional dollar of income is taxed at your marginal rate. A large Roth conversion can push part of your income into a higher bracket, meaning some of the converted dollars may be taxed at a higher rate than you expected.

This is why many people spread conversions over several years instead of converting everything at once. A common approach is "bracket filling," which means converting just enough each year to use up the remaining room in your current tax bracket without crossing into the next one.

State income taxes matter too. Depending on where you live, a conversion may also increase your state tax bill, and moving to a lower-tax state later could change whether converting now makes sense.

Roth Conversions and Medicare Premiums (IRMAA)

If you are enrolled in Medicare or will be soon, a Roth conversion can affect what you pay for Part B and Part D coverage. Higher-income beneficiaries pay an Income-Related Monthly Adjustment Amount, known as IRMAA, on top of standard premiums.

IRMAA is based on your modified adjusted gross income from two years earlier. That means a conversion you complete this year could increase your Medicare premiums two years from now. Because IRMAA works in tiers, going even one dollar over a threshold can trigger the higher surcharge for that tier for the entire year.

This two-year lookback also matters for people in their early 60s. Conversions done at age 63 or later can affect premiums once Medicare coverage begins.

How a Roth Conversion Can Affect Social Security Taxation

Up to 85% of your Social Security benefits may be taxable, depending on your "provisional income," which includes your adjusted gross income, tax-exempt interest, and half of your Social Security benefits.

Because conversion income increases your adjusted gross income, it can cause more of your Social Security benefits to become taxable. In some cases, this creates a higher effective tax rate on the conversion than your bracket alone would suggest, since each additional dollar of income can pull more benefit income into the taxable column.

This is one reason some retirees choose to complete conversions before they start claiming Social Security.

Other Tax Benefits and Subsidies That Can Be Affected

Many tax provisions phase out or change as income rises. A Roth conversion can reduce or eliminate eligibility for benefits such as:

Health insurance premium tax credits. If you buy coverage through the Affordable Care Act marketplace before Medicare eligibility, your premium subsidy is tied to your income. A conversion could reduce your subsidy or eliminate it.

The 0% long-term capital gains rate. Lower-income taxpayers may pay 0% on qualified dividends and long-term capital gains. Conversion income can push those gains into the 15% bracket.

The Net Investment Income Tax. The conversion itself is not investment income, but it raises your modified adjusted gross income, which could expose your investment income to the additional 3.8% tax.

Income-based deductions and credits. Several deductions and credits, including the additional deduction for taxpayers age 65 and older created in 2025, phase out at higher income levels.

College financial aid. For families with students applying for aid, a conversion can increase reported income and potentially reduce aid eligibility.

Paying the Tax: Why Outside Cash Matters

One of the most overlooked parts of a Roth conversion strategy is how you pay the tax.

Ideally, the tax is paid with cash from a taxable account or savings. This lets the full converted amount stay invested in the Roth IRA, where it can grow tax-free.

If you instead withhold tax from the conversion itself, less money ends up in the Roth, which reduces the long-term benefit. If you are under age 59½, the amount withheld for taxes may also be treated as an early distribution and subject to a 10% penalty.

Timing matters as well. Because conversion income may not have tax withheld, you may need to make estimated tax payments during the year to avoid underpayment penalties.

Roth Conversions Can't Be Undone

Before 2018, taxpayers could "recharacterize" a Roth conversion and reverse it if circumstances changed, such as a market decline after converting. That option no longer exists. Once you convert, the decision is final, which makes careful planning before you convert especially important.

It's also worth knowing that each conversion has its own five-year holding period for penalty purposes if you are under 59½. Withdrawing converted funds too soon could trigger a 10% penalty.

When a Roth Conversion May Make Sense

Despite the potential costs, a Roth conversion can be a smart move in the right situation. It may be worth considering if:

• You're in a temporarily low-income year, such as after retiring but before Social Security and RMDs begin.
• You expect to be in a higher tax bracket later, whether from RMDs, pension income, or future tax law changes.
• You have cash outside your retirement accounts to pay the tax.
• You want to reduce future RMDs or leave tax-free assets to heirs, especially if your beneficiaries are likely to be in higher tax brackets than you.
• You have deductions or losses in a given year that could offset some of the conversion income.

Building a Roth Conversion Strategy That Fits Your Whole Plan

The right Roth conversion strategy looks at multiple years, not just this one. A thoughtful plan considers your current and expected future tax brackets, when you'll claim Social Security, when Medicare begins, how RMDs will affect your income later, your estate planning goals, and where the money to pay the tax will come from.

Running projections before converting can help you see not only the tax on the conversion itself, but also the indirect effects on premiums, benefits, and deductions. Often, the best answer is a series of smaller, well-timed conversions rather than one large one.

Frequently Asked Questions About Roth Conversions

Is there an income limit for Roth conversions?
No. Anyone with a traditional IRA or eligible pre-tax retirement account can convert to a Roth IRA, regardless of income.

Can a Roth conversion increase my Medicare premiums?
Yes. Medicare uses your income from two years earlier to determine IRMAA surcharges, so a large conversion could increase your Part B and Part D premiums two years later.

Should I pay the tax on a Roth conversion from the IRA?
Generally, paying the tax with outside funds is more efficient because more money stays invested in the Roth. If you're under 59½, using IRA funds to pay the tax may also trigger a 10% penalty on the amount withheld.

Can I reverse a Roth conversion?
No. Recharacterizations of Roth conversions were eliminated starting in 2018, so conversions are permanent.

How much should I convert each year?
It depends on your tax bracket, other income, and goals. Many people convert just enough to stay within their current bracket or below key thresholds, such as IRMAA tiers.

The Bottom Line

A Roth conversion can be a powerful tool for creating tax-free income in retirement, but the true cost goes beyond the tax on the converted amount. Before converting, consider how the added income could affect your tax bracket, Medicare premiums, Social Security taxes, and eligibility for other benefits, and make sure you have a plan to pay the tax.

Working with a financial professional or tax advisor can help you evaluate whether a Roth conversion makes sense and how to structure it to fit your broader financial plan.

This article is for informational purposes only and does not constitute tax, legal, or investment advice. Tax laws change frequently, and individual circumstances vary. Consult a qualified professional before making decisions about your retirement accounts.