For most of your working life, you don’t get to pick your tax bracket. Then you retire — and for a few years, that changes.
In the gap between your last paycheck and Social Security, income largely disappears. No wages, no benefits, no forced withdrawals yet. For many early retirees, taxable income drops to the lowest it will ever be again.
That’s the Roth conversion window. Many people sail through it without doing a thing. The ones who don’t can move money into a Roth at rates they’ll never see again.
Why the window slams shut
The window closes for a simple reason: the income sources that were switched off come back on, one after another, and they don’t switch off again. Three forces do the work.
Social Security switches on
Claiming adds a stream of income back to your return and lifts you out of the trough — but the sharper problem is what it does to the benefit’s own tax treatment.
- Once your provisional income clears the upper thresholds — $34,000 for single filers, $44,000 for couples filing jointly — up to 85% of your Social Security benefit becomes taxable. Those thresholds haven’t been adjusted for inflation since 1994, so more retirees cross them every year.
- That’s why conversions run after you claim are clumsier: the added income can drag more of the benefit into the taxable column at the same moment.
Required distributions begin and stack on top
At 73 or 75, depending on your birth year, the IRS forces withdrawals out of your traditional accounts whether you need the money or not — and they land on top of Social Security, not instead of it. The part people misread is where the pressure comes from. There’s no “rates jump” deadline baked into the law as it stands: the 2025 tax law (the One Big Beautiful Bill Act) removed the scheduled sunset of the seven-bracket structure, so the brackets aren’t currently set to snap higher. But that’s today’s law — a future Congress can change rates, which is its own reason not to assume today’s low brackets will wait for you. The clock isn’t the tax code — it’s your own income climbing back up and pushing you into brackets you’d briefly escaped.
The survivor's penalty
When one spouse dies, the survivor usually shifts from married-filing-jointly to single — often on a similar amount of income, but with narrower brackets and a standard deduction roughly half the size ($16,100 versus $32,200 in 2026). The same income, taxed at a higher effective rate. A conversion strategy run during the window is partly insurance against exactly this: every dollar moved to Roth now is a dollar the survivor won’t be taxed on later.
What a Roth conversion actually does
You’re not spending the money or changing how it’s invested — you’re changing its tax status. Traditional dollars get taxed later, at whatever rate applies then; Roth dollars, by contrast, generally aren’t taxed again on qualified withdrawals under current law. (A withdrawal is “qualified” once the account has been open at least five years and you’re 59½ or older, with a few exceptions; converted amounts carry their own separate five-year clock.)
The reason to do it during the window is the whole point of this article: you’re choosing to be taxed now, while your rate is unusually low, instead of later, when Social Security and required distributions have pushed it back up.
Filling the empty brackets
The goal isn’t to convert everything. It’s to convert just enough to fill up the low brackets you’d otherwise leave empty — then stop before you spill into the next one.
Here’s the 2026 schedule for a married couple filing jointly, applied to taxable income (that is, after the $32,200 standard deduction):
- 10% — up to $24,800
- 12% — $24,801 to $100,800
- 22% — $100,801 to $211,400
- 24% — $211,401 to $403,550
For single filers, the 12% bracket ends at $50,400 and the 22% bracket at $105,700.
The two natural “stop here” lines for most retirees are the top of the 12% bracket and the top of the 22% bracket. Convert up to one of those ceilings, and every converted dollar is taxed at that rate or lower — and not a dollar more.
A worked example
Consider a hypothetical couple, both 64, retired and not yet claiming Social Security. Say that after the standard deduction their taxable income for the year is about $20,000 — some dividends and interest, nothing else. (This illustration shows the mechanics only. It assumes federal tax alone, a single tax year, and that they pay the conversion tax from money held outside the IRA. Your own numbers will differ.)
- The top of their 12% bracket sits at $100,800 of taxable income.
- That leaves roughly $80,000 of room to convert at 12% or lower.
- The top of the 22% bracket, at $211,400, leaves about $190,000 of room — which, depending on the size of their accounts, may still sit below the rate their future required distributions could trigger.
In this scenario, converting $80,000 would cost them roughly $9,500 in federal tax this year, most of it at 12%. In exchange, that $80,000 — and whatever it grows to — can later be withdrawn tax-free if the withdrawal is qualified, won’t count toward the provisional-income test that taxes Social Security, and won’t resurface as a required distribution, all under current law.
Why the Roth side keeps paying off
Once the money is in a Roth, three things shift in your favor:
- No lifetime required distributions. Under current law, a Roth IRA has no RMDs during the original owner’s lifetime, so the balance can stay invested rather than being forced out — though its value still rises and falls with the markets.
- Tax-free withdrawals that stay out of the other formulas. Qualified Roth withdrawals generally aren’t taxed, and they don’t count toward the provisional-income test that taxes Social Security or the income figure that sets Medicare premiums.
- A potentially cleaner inheritance. Heirs generally receive Roth dollars tax-free, whereas a traditional balance typically hands them a tax bill — though most non-spouse heirs must still empty the inherited account within 10 years.
Done well, a conversion doesn’t just change when you pay tax. It can shrink the future income that could otherwise inflate everything from your Medicare premiums to your surviving spouse’s tax bracket.
The traps that wreck the math
The window is real, but it doesn’t exist in isolation. A poorly sized conversion can spike Medicare premiums two years out, pull more Social Security income into the taxable column, or reduce a deduction the retiree didn’t know they were relying on. These interactions are worth understanding before converting — not after.
The IRMAA cliff
Medicare surcharges are calculated from MAGI two years prior and operate on a cliff structure rather than a graduated one. For 2026, the first surcharge tier begins at $109,000 for single filers and $218,000 for couples filing jointly. Crossing a threshold by any amount may trigger the full surcharge for that tier — a meaningful jump per person in Part B premiums alone, with additional surcharges on Part D. For couples where both spouses are on Medicare, the annual cost can add up quickly.
Mapping planned conversions against IRMAA tier boundaries — and sometimes stopping short of a bracket ceiling to avoid a cliff — is one of the more consequential planning decisions in this space.
Social Security taxation and the senior deduction
For retirees already claiming Social Security, conversion income stacks on top of the benefit and may push more of it into the taxable column. The provisional-income thresholds — $34,000 for single filers, $44,000 for joint filers — mark the point where up to 85% of Social Security may become taxable, and those thresholds haven’t been inflation-adjusted since 1994.
The temporary senior deduction (available through 2028) adds another layer. Worth up to $6,000 per filer, it begins phasing out at $75,000 of MAGI for single filers and $150,000 for joint filers. A large conversion can reduce or eliminate it entirely, making the effective marginal cost of conversion income potentially higher than the bracket rate alone would suggest.
For pre-65 retirees: ACA subsidies
Retirees not yet on Medicare who rely on ACA marketplace coverage should be aware that conversions increase MAGI, which determines subsidy eligibility. Pushing income past certain thresholds can reduce or eliminate premium tax credits — sometimes generating a repayment at tax time that significantly changes the overall cost of the conversion.
Before you start: it cannot be undone
The Tax Cuts and Jobs Act permanently eliminated the ability to reverse a Roth conversion through recharacterization for any conversion made after January 1, 2018. There is no mechanism to undo it after the fact, regardless of what happens to account values or your tax situation. That makes sizing and timing decisions more consequential than they once were, and generally argues for converting thoughtfully across multiple years rather than all at once.
This article covers federal tax only. Many states also tax Roth conversions as ordinary income; the impact varies considerably by state.
Who this is and isn't for
Roth conversions during the window aren’t universally beneficial — the case depends on a few structural factors that vary considerably from one retiree to the next. This section isn’t a suitability determination; it’s a set of conditions that tend to change the math in one direction or the other.
Factors that generally strengthen the case
The clearest candidates tend to share a few characteristics: a large traditional IRA or 401(k) balance relative to other assets, a genuine income gap between retirement and the start of Social Security or RMDs, and reason to expect their future tax rate will be at least as high as it is now. That last point often follows from the first — large tax-deferred balances typically generate large required distributions later, which stack on top of Social Security and can push a retiree into a bracket well above where they sit during the window. The surviving-spouse scenario reinforces this: a large traditional balance inherited by a single filer tends to produce a significantly higher effective rate than the couple faced together.
Having cash outside the IRA to pay the conversion tax also matters. Paying from outside preserves the full converted amount inside the Roth; paying from the IRA itself reduces what moves over and may carry additional costs depending on the retiree’s age and account type.
Factors that may weaken it
The case tends to be weaker when the income gap is small or doesn’t exist — if retirement income is already substantial, there may be no low-bracket room to fill. Similarly, retirees with significant charitable intent may find that qualified charitable distributions from a traditional IRA accomplish comparable goals without triggering a taxable conversion.
If future income is expected to be meaningfully lower — because of downsizing, no pension, or modest account balances — the rate on future withdrawals may simply not be high enough to justify paying tax now. And for pre-65 retirees where ACA subsidies are material, the interaction with conversion income deserves careful attention before proceeding.
As with everything in this article: the factors above are general considerations, not a substitute for reviewing your own return with a qualified tax advisor.
How to think about sizing it
There’s no formula here — and any tool or article that offers one is oversimplifying. The right conversion amount in a given year depends on income, account balances, Medicare situation, Social Security timing, state taxes, and variables that interact in ways that are impossible to generalize. What follows are principles for framing the decision, not a prescription for making it.
A few things tend to matter most:
- Start with the bracket ceiling, not the account balance. Identify where your taxable income sits, find the room remaining before the next bracket, and consider stopping there. Which ceiling to target — 12%, 22%, or higher — depends on account size, years remaining in the window, and expected income once RMDs and Social Security begin.
- Check the IRMAA boundary separately. The bracket ceiling and the IRMAA threshold are different lines. In some cases the Medicare cliff should be the binding constraint, not the tax rate. Running both calculations before year-end — when there’s still time to adjust — is more useful than working backward in April.
- Think in years, not one lump sum. A multi-year approach tends to smooth the tax cost and allows for recalibration as income and account values change. Concentrating conversions in the earliest years of the window, when income is lowest and time for Roth growth is longest, is a reasonable general orientation — though individual circumstances vary considerably.
This is where general education ends and personalized advice begins. The principles above can help frame a conversation with a tax or financial advisor; the actual number requires looking at an individual return.
Make the most of the window
The concept isn’t complicated. What’s hard is the execution — knowing how much to convert, in which years, against everything else competing for the same dollars: Medicare premiums, Social Security timing, the senior deduction, state taxes, and a market that doesn’t hold still while you plan.
If you’d like to explore how coordinated tax and investment planning might apply to your retirement situation, you can request a Fit Meeting with Paul Axberg at Axberg Wealth Management. This introductory conversation is designed to review your priorities, discuss potential strategies, and determine whether working together is an appropriate mutual fit — without assumptions or commitments.
Disclosures
Content provided through a collaboration with Paul Axberg and Schnebly Hill Digital Marketing. This content was generated using the help of AI research, and is intended for informational purposes only. Please consult a qualified professional for personalized advice. For specific estate planning advice, please consult a qualified estate planning attorney.