People spend a lot of energy asking whether to do Roth conversions. The better question — once you've decided they make sense — is how much.
Convert too little and you leave years of tax savings on the table. Convert too much and you push income into a steeper bracket, trigger higher Medicare premiums, or create a tax bill you weren't ready for. The goal is finding the amount that threads that needle, year after year.
It sounds complicated. The mechanics aren't, once you know what you're looking at.
Start With Your Tax Bracket
Every dollar you convert from a traditional IRA to a Roth gets added to your taxable income for that year. So the first question is: what rate will you pay on those extra dollars?
Here are the 2026 ordinary income brackets for married couples filing jointly:
| Rate | Taxable Income (MFJ) |
|---|---|
| 10% | $0 – $24,800 |
| 12% | $24,801 – $100,550 |
| 22% | $100,551 – $206,700 |
| ⚠ First IRMAA tier begins at $218,000 MAGI — only $11,300 above the top of the 22% bracket | |
| 24% | $206,701 – $394,600 |
| 32% | $394,601 – $501,050 |
| 35% | $501,051 – $751,600 |
| 37% | Over $751,600 |
The goal for most retirees is to convert up to — but not past — the top of a given bracket. Fill the 22% bracket before you let dollars spill into 24%. Fill the 12% bracket before you let dollars spill into 22%.
The question is: how much room do you have left in your current bracket after accounting for Social Security, pension income, RMDs, and anything else already pushing your income up?
Example: You're married, your combined income from Social Security and a small pension is $72,000, and your standard deduction of $32,200 brings taxable income to roughly $40,000. The top of the 22% bracket is $206,700. That leaves about $166,000 of room before you hit 24%.
You probably don't convert all of that. But you might convert $50,000 or $70,000 and stay comfortably inside the 22% bracket — while keeping a close eye on that IRMAA threshold just above.
Don't Forget About IRMAA — And How Close It Is
Here's where a lot of retirees get surprised: your Medicare Part B and Part D premiums are based on your income from two years prior. Go over certain thresholds and you'll pay surcharges — called IRMAA — on top of your base premium.
In 2026, the first IRMAA tier kicks in at $218,000 of modified adjusted gross income for married couples filing jointly. For individuals, it's $109,000.
Look at that bracket table again. The top of the 22% bracket for married couples is $206,700. The first IRMAA cliff is $218,000. That's a gap of roughly $11,300 — barely enough to cover a modest conversion before you're in IRMAA territory. Anyone converting aggressively to fill the 22% bracket needs to be watching both numbers simultaneously, or they'll find themselves with a Medicare premium surprise two years down the road.
The cliff is real. IRMAA isn't a sliding scale — it's a step function. One dollar over $218,000 and you owe the full surcharge for that tier. For a married couple where both spouses are on Medicare, that first IRMAA tier adds roughly $2,300 per year in premiums. It doesn't mean you stop converting. It means you model it deliberately and decide whether the long-term tax benefit outweighs the short-term premium cost.
Your Future Tax Rate Is the Other Side of the Equation
Roth conversions are a bet on your future tax rate being higher than your current one. If you'll be in the same bracket either way, the math gets murkier — though Roth still offers other advantages, like no required minimum distributions and tax-free growth. But the future-rate question goes beyond just your own situation. If you have heirs who will inherit a traditional IRA, they face the IRS's 10-year withdrawal rule: the entire account must be distributed within 10 years of your death. For working-age children in their peak earning years, that forced income can land squarely in their highest tax brackets. Roth conversions done today pass tax-free assets to the next generation instead of a ticking tax bill.
A few things tend to push future rates higher:
Required Minimum Distributions. Once you hit 73, the IRS requires you to start drawing from your pre-tax accounts — whether you need the money or not. Large traditional IRAs generate large RMDs, which stack on top of Social Security and can push you into higher brackets with no flexibility to manage it.
The surviving spouse problem. When one spouse passes, the survivor files as a single taxpayer. Same income, narrower brackets. What was taxed at 22% for a married couple can quickly become 32% for a single filer. Conversions done while both spouses are alive can reduce the IRA balance before that happens.
Where taxes are likely headed. Current rates are near historical lows. The U.S. is carrying a level of national debt that, by any honest measure, will eventually require higher tax revenue to service. There's no guarantee of when or how, but the direction of travel seems reasonably clear. Paying tax now, at known rates, rather than betting on favorable policy for the next 20 years is a defensible position.
The Pension and Social Security Problem
There's a group of retirees who tend to have the largest unconverted IRA problem: those with generous governmental pensions combined with Social Security. The pension covers living expenses. Social Security covers the rest. They never need to touch the IRA — so they don't. The account keeps growing, untouched, for years.
It sounds like a good problem. It isn't. Every year that passes without a conversion is another year the pre-tax balance compounds — and another year of missed opportunity to convert at lower rates before RMDs begin. When the RMD clock eventually starts, these retirees often face the largest forced distributions of anyone, because their IRA has had decades to grow without interruption. Combine that with pension income, Social Security (up to 85% of which is taxable), and an RMD that they genuinely don't need, and suddenly they're in a higher bracket than they ever were while working.
If this describes you — income covered, IRA untouched — the window between now and age 73 is exactly the time to be running Roth conversion projections.
A Practical Framework
Project your taxable income for the year from all sources: Social Security, pensions, dividends, RMDs if applicable, and any other income.
Subtract your standard deduction ($32,200 for married filing jointly in 2026) to get estimated taxable income.
Identify the top of your current tax bracket. Calculate how much room remains before you hit the next bracket.
Check IRMAA thresholds against your total MAGI — including the conversion amount. If you're already near $206,700 in taxable income, you may have little or no room before hitting the $218,000 IRMAA cliff. Run both numbers before deciding on the conversion amount.
Run the conversion amount through a planning tool to confirm the tax cost, then compare it to the expected benefit: lower RMDs, a larger tax-free pool, reduced exposure to future rate increases, and — if relevant — a cleaner inheritance for your heirs.
If possible, pay the conversion tax from non-retirement funds. Pulling from the IRA itself to cover the bill reduces the amount actually getting to Roth — and adds more taxable income in the same year.
There's No One Right Number
The honest answer is that the right conversion amount changes every year. It depends on your income, your bracket, your Medicare situation, your IRA balance, how long you expect to live, and what you think will happen to tax policy over time.
Some years you might convert $20,000. Other years, $80,000. Some years — if you have a large capital gain, or one spouse has significant income from part-time work — you might convert nothing and wait.
What doesn't change is the logic: you're trying to pay tax now, at a known rate, instead of paying it later at an unknown one. The goal is to fill low-rate brackets deliberately, over time, rather than letting RMDs do it for you at whatever rate Congress decides next.
Done well, Roth conversions are one of the most reliable ways to reduce your lifetime tax bill. Done carelessly — converting without looking at brackets, ignoring IRMAA, or paying the tax from the IRA itself — they can cost more than they save.
The number matters. So does the process.
