Investing & Retirement · July 30, 2026 · 7 min read

The Roth conversion window between retiring and RMDs

Key takeaways

While you're working, your salary sets your tax bracket. Once Social Security and required withdrawals start, those set it. In between there are a handful of years where you set it yourself.
The window opens with your last paycheck and closes when required minimum distributions begin, which is age 73 if you were born between 1951 and 1959, and 75 if you were born in 1960 or later.
A married couple, both 65 or older, can move $148,300 out of a traditional IRA and into a Roth in 2026 and pay about $11,600 in federal tax. That's an effective rate of 7.8%.
Leaving $1.5M alone from 64 to 75, growing at 6%, turns it into about $2.85M and produces a first required withdrawal near $115,700, whether you want the money that year or not.
The window has a ceiling. Medicare surcharges start at $218,000 of income for a couple and are based on your tax return from two years earlier, so income at 63 shows up in your premium at 65.

For your entire working life, your tax bracket has been a function of your salary. Sure there's some wiggle room by putting more money into your 401(k) or funding an HSA, but for the most part your tax bill was decided by your employer year over year.

On the far end of retirement, you again lose some of your ability to control your tax bracket. First comes Social Security. Then you're required to take withdrawals from your traditional accounts. Both create ordinary income, and while you could take more from your accounts if needed beyond the required minimum distribution (RMD), you're not allowed to take less.

Between those two periods of your life, there are a number of years where your income and tax bracket are in your control. If you've stopped working, delayed Social Security, and aren't old enough for required withdrawals, your taxable income can sit near zero. That's the stretch where a Roth conversion lets you move money out of your traditional accounts at a rate you choose, instead of being at the mercy of the IRS again.

The time-frame you control

The opening date for this window of opportunity is your last paycheck, and the closing date is the year you turn 73 or 75, depending on your birth year. Born 1951 through 1959, required withdrawals start at 73. Born 1960 or later, they start at 75. Congress has moved the age twice in recent years.

Those two dates determine how long the window stays open. The date you start taking Social Security starts to close the window, but not all the way. Each year you wait past your full retirement age raises the benefit by about 8%, and it's also a year with no benefit landing in your income, which leaves the low brackets sitting open for Roth conversions.

Someone born in 1963 who stops working at 63 has 12 years. Someone born in 1957 who works until 65 has 8. So I think it's worth knowing what you're working with as a precondition to planning the numbers out.

What one of those years is actually worth

Take a married couple filing jointly in 2026, both 65 or older, with no wages and no Social Security yet.

Their deductions stack up to $47,500. That's the $32,200 standard deduction, plus $1,650 each for being over 65, plus the $6,000 per person senior deduction that came out of the 2025 tax law (and is scheduled to expire after 2028).

The 12% tax bracket runs to $100,800 of taxable income. Add the deduction buffers and they could convert $148,300 from a traditional IRA to a Roth and still land at the top of the 12% bracket.

The federal tax on that is $11,600. On $148,300 moved, that's an effective rate of 7.8%. In Arizona, add the flat 2.5% state rate.

Now think about the rate those dollars avoided on the way in. Contributions made while you were earning $250,000 or $350,000 skipped tax at 24%, 32%, or higher. Moving them out at 7.8% is the whole idea. You deferred at one rate and you're paying at another, and you get to pick the year.

Once the money is in the Roth, there's no more tax to pay, and there are no required minimum distributions.

The constraints

Filling a bracket is only part of the calculation. Two other thresholds sit below the top of the 22% bracket, so one of them is usually what caps the conversion. Which one depends on whether you're on Medicare yet.

Medicare surcharges. Once you're on Medicare, your premium is set by your income from two years earlier. For a couple in 2026, the first surcharge tier starts at $218,000, and crossing it costs about $2,300 for the year across both spouses. One dollar over the line triggers the entire amount.

The 22% bracket for a married couple runs to $211,400 of taxable income, which after deductions is well past $218,000 of total income. So a conversion sized to fill the 22% bracket puts you into the surcharge. From 63 on, the Medicare threshold is the ceiling that binds first, and the bracket is beside the point.

Marketplace health insurance. If you retire before 65, you're typically responsible for your own coverage until Medicare starts. The enhanced subsidies expired at the end of 2025 and Congress is still arguing about whether to bring them back, so as it stands 2026 has a hard cutoff at 400% of the federal poverty level, roughly $84,600 for a household of two. A Roth conversion raises the income figure that cutoff measures dollar for dollar, and a dollar over it wipes out the entire year's credit. For a couple around 60 sitting just above that line, the difference between a subsidized premium and the full benchmark premium runs into five figures for the year.

Both cutoffs measure modified adjusted gross income (MAGI), and this is where a Roth account earns its keep a second time. Distributions from a Roth are excluded from MAGI entirely. Money you convert during the window comes back out later without moving you toward either of these constraints.

The bill that eventually comes due (if you do nothing)

Say that same couple leaves a $1.5M traditional balance alone from 64 until required withdrawals begin at 75. At 6% growth it becomes about $2.85M.

Using IRS math on the required minimum distribution when they hit 75, that's about $115,700 of ordinary income in a single year. Year over year, they'll be required to take distributions, whether they need them or not, and recognize that income.

Then there's Social Security income on top of that. A couple who both delayed to 70 might see $80,000 a year in combined benefits by then. Now you're near $196,000 of income at 75, in the 22% bracket, with 85% of your Social Security taxable and your Medicare premiums climbing.

This is all to illustrate that the gap between retirement and starting RMDs provides an opportunity to reduce the "RMD bomb" that comes if your IRA balance grows faster than you're spending. The couple who converted through the window shows up at 75 with a smaller traditional balance, a smaller required withdrawal, lower taxes, and tax-free distributions for the rest of their life.

Plan this before December if you're able

A conversion squeezed into the last week of December leaves no room to fix anything, and a few things about these are unforgiving.

You can't undo it. Until 2018 there was the possibility to reverse a Roth conversion. That's no longer an option. Whatever you convert is irreversible.

Watch the custodian withholding. Custodians default to withholding on IRA distributions, and a Roth conversion is technically a distribution. Every withheld dollar is a dollar that leaves the IRA and never arrives in the Roth. The general idea is to pay the tax from a brokerage account, or cash funds, and let the full amount land where it can grow tax-free.

A conversion in the 12% bracket can actually cost you 27%. Long-term capital gains are taxed at 0% up to $98,900 of taxable income for a couple in 2026. Ordinary income from a conversion fills that space first and pushes your gains up into the 15% rate. So the conversion costs 12% on its own dollars plus 15% on the gains it displaced. Any year with both capital gains and a conversion in it needs that math run before you pick the conversion amount.

The tax isn't withheld, so you owe it as you go. A conversion in a year with no paycheck usually means making an estimated payment, and a missed one turns into a penalty on a return you weren't expecting to owe on.

Start before you need to

To sum up, this window of opportunity is book-ended by two dates: the year you stop working, and the year you hit RMD age. Depending on when you retire, you could have a decade or more to smooth out your lifetime tax bill through Roth conversions.

Both of those dates are on the calendar already, so the planning doesn't have to wait for retirement to arrive. Knowing the size of the window a few years out is what lets you decide how much to convert in the first year rather than working it out in a hurry the following December.

Much of retirement planning depends on things nobody can predict. This window isn't one of them, and I think that makes it worth using.