What Is a Roth Conversion and When Does It Make Sense?

If you've spent any time reading about retirement tax planning, you've probably come across the term "Roth conversion." You may have gathered that it's generally considered a useful strategy, but you're not entirely sure what it involves or whether it's relevant to your situation.

The part that trips people up at first is this: a Roth conversion means voluntarily paying taxes you don't technically owe yet. That feels counterintuitive. Nobody enjoys writing a check to the IRS before they have to. So there has to be a reason it might be worth doing, and for many people in the right circumstances, there can be.

What a Roth Conversion Actually Is

The basic process is straightforward. Money moves from a pre-tax retirement account — typically a traditional IRA or a 401(k) that's been rolled into a traditional IRA — into a Roth IRA. The amount converted gets added to taxable income for the year the conversion is made and consequently taxes are owed. 

In exchange, that money grows tax-free from that point forward. Qualified withdrawals in retirement are tax-free. And unlike traditional IRAs, Roth IRAs are not subject to required minimum distributions during the owner's lifetime. In essence, it's settling the tax bill today in exchange for complete tax freedom on that money going forward.

The Silent Partner in Your IRA

Here's a way to think about a traditional IRA that can shift the perspective a bit: a portion of the money in that account was never really the account holders to keep.

Every dollar that went in pre-tax came with an implicit agreement. The government allowed the taxes to be deferred, but it didn't forgive them. Whatever the future tax rate turns out to be, that percentage of the balance belongs to the IRS. They're going to collect it — either through voluntary withdrawals or through required minimum distributions.

For someone in a meaningful tax bracket, a significant portion of a traditional IRA balance isn't theirs. It's the government's share, sitting in the account, growing alongside the rest.

A Roth conversion is essentially a buyout of that silent partner. It means paying the government's share now, at today's known rate, and moving the remaining balance into an account that belongs entirely to the account holder. No more uncertainty about what future rates might be. No more watching that embedded liability grow larger every year.

One important consideration that planners often emphasize: the math tends to work much better when the tax bill is paid from money outside the IRA — a checking account, a taxable brokerage account, cash savings. Paying the taxes from the IRA itself reduces the amount that actually makes it into the Roth, which can undermine much of the benefit. And for anyone under 59½, the amount used to cover the tax could also be subject to a 10% early withdrawal penalty. The goal is to move the full converted amount into the Roth and settle the tax bill separately.

The Conversion Window Most People Don't Know About

For many people approaching or entering retirement, a window opens up — sometimes for just a few years — where Roth conversions may be done at the lowest tax rate they'll see for the rest of their lives.

When someone retires, income naturally drops. If they haven't yet started Social Security and aren't yet required to take RMDs, their taxable income during those years may be remarkably low — perhaps just some investment income, a small pension, or drawdowns from a taxable account. They may be sitting in a low bracket with meaningful room to spare.

That window tends to close once Social Security benefits begin, and it narrows further when RMDs kick in. At that point, those income sources stack on top of each other, filling up lower brackets and pushing additional income — including any conversions — into higher ones. A conversion that could have been done at a lower rate during the window might cost meaningfully more once that window shuts.

A Quick Example

Consider a hypothetical retiree — let's call her Sarah — who retires at 63 with $1.8 million in a traditional IRA. She plans to start Social Security at 67 and will be subject to RMDs at 75. Between 63 and 67, her taxable income is relatively modest — some dividends and a small pension that keep her in the lower brackets.

During those four years, Sarah may have meaningful room in a favorable bracket to convert portions of her IRA to a Roth each year. Once Social Security begins at 67, that bracket space shrinks. Once RMDs start layering on at 75, it may shrink further — and conversions at that point could push income into a noticeably higher bracket.

There's also a hidden cost worth knowing about. Medicare premiums are based on income from two years prior, so a large conversion in one year could trigger IRMAA surcharges — higher Medicare Part B and Part D premiums — two years down the road. This doesn't necessarily make conversions a poor choice, but it's a cost that benefits from being factored into the analysis.

This Isn't an All-or-Nothing Decision

Roth conversions don't have to happen all at once. In fact, a multi-year approach — converting a targeted amount each year to fill a specific bracket without spilling into the next one — is how this strategy is most commonly implemented. It's a precision exercise, not a one-time event.

Getting it right involves looking at the full picture: current and projected income, tax bracket thresholds, Medicare IRMAA thresholds, Social Security timing, state taxes, and the availability of outside funds to cover the tax bill. This is an area where the interaction between variables is complex enough that working with a qualified advisor can add meaningful value.

The Widow's Penalty

There's one more dimension to Roth conversions that doesn't get enough attention: what happens when one spouse passes away.

When a couple loses a partner, the surviving spouse typically shifts from filing jointly to filing as a single taxpayer. The single-filer brackets are roughly half the width of married-filing-jointly brackets, which means the survivor can find themselves in a higher tax bracket even though their income hasn't changed much — and in some cases has actually decreased.

This is sometimes called the widow's penalty, and it can create a meaningful and lasting increase in the surviving spouse's tax burden. Roth conversions done during the years when both spouses are alive — particularly during the low-income window discussed above — can help reduce the size of the traditional IRA balance that will eventually generate taxable RMDs for the surviving spouse. It's one of those planning considerations that's easy to overlook but can make a real difference for the partner who's left managing finances alone.

The Bigger Picture

A Roth conversion is one of the more powerful tools in the retirement tax planning toolkit, but its value depends heavily on timing, amounts, and how it fits within a broader strategy.

For anyone approaching retirement with significant pre-tax balances, understanding whether this window exists, and how wide it might be, is worth exploring sooner rather than later. The window doesn't stay open forever, and once it closes, the opportunity to “settle up” at today's rates may not come around again.

Tad Jakes, CFP®, EA, ECA

The scenarios described in this article are hypothetical and are presented for educational and illustrative purposes only. This content is intended for general informational purposes and does not constitute personalized financial, tax, or legal advice. Tax laws and retirement plan rules are subject to change. Please consult a qualified financial advisor or tax professional regarding your specific situation.