Roth Conversions Explained: When Converting Makes Sense (and When It Doesn't)

The same $50,000 conversion costs anywhere from about $5,900 to nearly $12,000 depending on your other income that year. Timing is the biggest lever.

Think of your traditional IRA like a deferred tax bill with an unknown interest rate. You got a tax break when you put the money in, but you'll owe income tax on every dollar you pull out. And you have no idea what tax rates will look like in 10 or 20 years. A Roth conversion is like locking in today's known rate instead of gambling on tomorrow's. If today's rate turns out to be lower, you win.

How the mechanics work

You move money from a traditional IRA (or roll over from a traditional 401(k)) into a Roth IRA. The converted amount gets added to your taxable income for the year. You pay ordinary income tax on it, at whatever your marginal rate happens to be. No special capital gains rate, no penalty. After that, the money grows tax-free and qualified withdrawals in retirement are completely tax-free.

There's no income limit on who can convert. Even people who earn too much to contribute directly to a Roth IRA can convert unlimited amounts from a traditional account. That's what makes conversions such a useful tool for higher earners.

Three reasons conversions can pay off

Tax-free growth compounds hard. When investments grow inside a Roth, you never share those gains with the IRS. A $100,000 conversion that doubles to $200,000 means $100,000 in gains that will never be taxed. In a traditional account, those same gains would face a tax bill of $22,000 or more at a 22% rate.

No Required Minimum Distributions. Traditional IRAs force you to start withdrawing at age 73 (rising to 75 in 2033 under the SECURE 2.0 Act), whether you need the money or not. Those RMDs can push you into higher tax brackets and increase Medicare premiums. Roth IRAs have no RMDs during your lifetime, so you keep full control over your taxable income in retirement.

Estate planning benefits. When heirs inherit a Roth IRA, they have to withdraw it within 10 years under current rules. But those withdrawals are tax-free. Inheriting a traditional IRA means the beneficiaries pay income tax on every dollar, potentially during their peak earning years.

The gap years window

For a lot of retirees, the years between stopping work and starting Social Security plus RMDs create an unusual opportunity. Picture someone who retires at 62 with $1.2 million in a traditional IRA. Their only income might be $30,000 from a taxable brokerage account. Without any conversion, they're barely using the 12% bracket.

But at 70, Social Security adds $35,000. At 73, RMDs add another $50,000 or more. Suddenly they're in the 22% or 24% bracket and locked in. The gap years are when you can fill lower brackets strategically, converting just enough to reach the top of the 12% or 22% bracket each year without spilling into higher rates. Across five to ten years, this can shift hundreds of thousands of dollars from "taxed at an unknown future rate" to "taxed at 12%."

The math comes down to a single question: is the tax you pay today less than the tax you'd pay on the same money (plus its growth) in the future?

This is why conversions can win even when future tax rates are similar to today's. You're paying tax on a smaller base now instead of a much larger base later. The longer the time horizon, the more that gap widens.

Patricia vs. David: two approaches

Two 62-year-olds, each with $800,000 in a traditional IRA and $30,000 in annual living expenses from other sources. Same situation, different strategies.

Both end up with a similar total balance. But Patricia converted $500,000 at an average rate of 12%, while David will pay 22–24% on his entire balance as he withdraws it. Over David's remaining retirement, that difference could exceed $100,000 in additional taxes. Money that stays in Patricia's family instead.

The pro rata rule and the 5-year clock

Pro rata rule: If you have both pre-tax and after-tax (nondeductible) contributions in your traditional IRAs, you can't cherry-pick which dollars to convert. The IRS treats all your traditional IRAs as one pool. If 90% of your total traditional IRA balance is pre-tax and 10% is after-tax, then 90% of any conversion is taxable. One common workaround: roll the pre-tax portion into a current employer's 401(k) if the plan allows it, leaving only after-tax money in the IRA.

5-year rule: Each conversion has its own 5-year clock. If you withdraw converted funds before age 59½ and before 5 years have passed since that specific conversion, you'll owe a 10% early withdrawal penalty on the taxable portion. After 59½, this penalty doesn't apply regardless of the 5-year clock. For most people considering conversions in their 60s, this is a non-issue. But if you convert before 59½, each conversion needs to be tracked separately.

Bracket-filling: the core method

The basic approach is to figure out how much room you have in your current tax bracket before hitting the next one, then convert exactly that amount. For 2026, a single filer in the 12% bracket can have up to $49,475 in taxable income. If your other taxable income is $15,000, you have $34,475 of conversion space at 12%. Every dollar over $49,475 gets taxed at 22%, which is an extra 10 cents on every dollar. For married couples filing jointly, the 12% bracket extends to $98,950 for 2026, which creates substantially more room.

Spilling a little into the next bracket isn't catastrophic. It just means the last chunk of your conversion costs more per dollar. The real mistake is converting so much in a single year that you push yourself into the 24% or 32% bracket when you could have spread it over two or three years at 12%.

A Roth conversion isn't a one-time decision. It's a multi-year strategy with several moving parts. Getting the details right can mean the difference between saving $30,000 and saving $150,000 over a lifetime.

The levers that matter

Conversion amount. Convert enough to fill your current bracket, but watch the boundary. Each bracket is a decision point. Converting $1 more than your bracket can hold costs an extra 10–12 cents in tax on that dollar.

Timing. Low-income years are conversion years. Job transitions, early retirement, sabbaticals, and the gap before Social Security and RMDs are the best windows. Once RMDs start, your floor income rises permanently.

Tax payment source. Paying the tax bill from taxable accounts (not from the converted funds) lets the full conversion amount grow inside the Roth. If you convert $50,000 and pay $6,000 in tax from the conversion itself, only $44,000 actually goes into the Roth. That $6,000 would have grown tax-free for decades.

Multi-year planning. Mapping out your projected income through age 75 or beyond lets you spot conversion space in each year. Social Security start dates, pension income, RMD projections, and any part-time work all factor in. Five years of $40,000 conversions almost always beats one year of $200,000.

When conversions don't make sense

You're already in a high bracket. If you're in the 32% or 35% bracket now and expect to drop to 22% or 24% in retirement, converting locks in the higher rate. The math works better when you wait until income drops.

You need the money within 5 years and you're under 59½. The 5-year rule and potential penalties make short-term conversions risky for younger converters. Even after 59½, the tax-free growth benefit needs time to overcome the upfront tax cost. Most analyses show a break-even period of 7–12 years.

You rely on ACA subsidies. Conversion income counts toward Modified Adjusted Gross Income. A large conversion could reduce or eliminate premium subsidies on marketplace health insurance, adding thousands to the effective tax cost.

You expect much lower future rates. If you plan to move to a state with no income tax, or expect minimal retirement income, traditional withdrawals might win. But keep in mind that federal tax rates can change, and RMDs create income floors that are hard to control.

Worth noting: large conversions can also trigger IRMAA surcharges on Medicare Part B and Part D premiums. For 2025, single filers with modified AGI above $106,000 (based on 2023 income) pay higher premiums. A conversion that pushes you over an IRMAA threshold could add $1,000 or more per year per person to Medicare costs. The thresholds work like cliffs, not gradual scales, so even a few dollars over the line triggers the full surcharge for that bracket.

The backdoor Roth (a related but different strategy)

High earners who exceed the Roth IRA contribution income limits (phaseout begins at $150,000 single / $236,000 MFJ for 2025) sometimes use a "backdoor" approach: contribute to a traditional IRA, then immediately convert to a Roth. This works best when you have no other traditional IRA balances, because the pro rata rule applies to all your traditional IRAs combined. It's annual maintenance, not a one-time conversion of accumulated funds.

What about starting late?

If you're already 70 with a large traditional IRA and RMDs approaching, the runway is shorter. But even 5–7 years of strategic conversions before RMDs begin can shift a meaningful portion of your balance to tax-free status. You're also reducing future RMDs, which has a compounding effect: lower RMDs mean more room for conversions each year. At some point the math may favor simply paying taxes as you go rather than accelerating them. Health, heirs' tax situations, state tax rates, and spending plans all influence where that point is.

What the 2025 tax law change means for conversions

The One Big Beautiful Bill Act (OBBBA), signed in 2025, made the Tax Cuts and Jobs Act brackets permanent — removing the sunset that was originally set for 2026. Before the OBBBA passed, much of the urgency around Roth conversions was driven by that impending deadline: convert now before rates go up. That deadline is gone, but the case for converting hasn't weakened. It has actually clarified.

Today's brackets are historically low compared to the pre-2017 rate structure (when the top marginal rate was 39.6%). There's no immediate deadline pressure, but there's also no reason to defer indefinitely. The longer you hold a large traditional IRA balance without converting, the more future RMDs take control of your taxable income away from you. The window for strategic, low-bracket conversions is still open — it just requires a longer-term plan rather than a year-end sprint.

One planning nuance the OBBBA introduced: several temporary enhanced deductions and credits created by the bill phase out at higher incomes. A large Roth conversion in 2025–2027 could reduce or eliminate some of those benefits. If you're in a year where you're receiving any OBBBA-created deductions, model the full tax picture — not just the marginal bracket — before deciding on a conversion amount.

Your optimal conversion strategy depends on your specific numbers: current income, traditional IRA balance, expected retirement income, and time horizon. The calculator below models different scenarios and shows how they affect your lifetime tax picture.

Quick Start Calculator

What to look for in the results

The tax cost of conversion is the immediate bill for converting this year. Compare that to your available cash in taxable accounts, since paying from outside the conversion is the ideal approach. The break-even year tells you when the tax-free growth in the Roth overtakes the upfront cost. If that year is beyond your time horizon, the conversion may not pencil out. Look at the projected RMD reduction to see how much your future required distributions decrease, which translates directly into more control over your taxable income later. And the lifetime tax savings is the bottom-line estimate: the total difference between converting and not converting, accounting for growth, withdrawals, and projected future rates.

This calculator provides estimates for educational purposes only. It uses simplified assumptions about tax brackets, growth rates, and future income that may not match your actual situation. Roth conversion decisions have significant tax consequences and may affect Medicare premiums, ACA subsidies, and other income-tested benefits. Tax laws change frequently. This calculator reflects general principles, not guarantees under current law.

Answers to the most common questions about Roth conversion rules, timing, and strategy.