Published May 1, 2026

The Roth Conversion Window: Pay Taxes Now So the IRS Can't Ambush You at 75

Let me start with something that doesn't get said plainly enough: every dollar sitting in your traditional IRA is not fully yours. A piece of it belongs to the IRS. They've agreed to let you hold it for a while. At age 75, that arrangement expires and they start taking their cut whether you want them to or not.

Those are called Required Minimum Distributions. They are not optional. You will pay tax on that money. The only real question is when and at what rate — and whether you get to decide, or the IRS does.

A Roth conversion is how you take control of that answer.

What a Roth Conversion Actually Is

Simple version: you move money from your traditional IRA (pre-tax) into a Roth IRA (after-tax). You pay ordinary income tax on whatever you move in the year you move it. After that, the money grows tax-free, comes out tax-free, and is never subject to RMDs for the original owner.

That's it. You're deciding to pay the tax now instead of later. The entire debate is whether "now" is cheaper than "later." In a lot of situations — especially for people who retire before 75 — it is.

You're not doing anything exotic. You're not exploiting a loophole. You're making a deliberate choice about when the IRS gets paid, on your terms instead of theirs.

Why the Gap Between Retirement and 75 Is the Sweet Spot

Think about your income in the years right after you retire. If you stop working at 62, you might not be drawing Social Security yet. Your pension may not have started. You're not taking RMDs. For a few years, your taxable income could be genuinely low — possibly lower than during your working years, and almost certainly lower than it will be at 75 when Social Security, pension, and RMDs are all stacking on top of each other at once.

That's the window. Your tax brackets have breathing room. Every dollar you convert from traditional to Roth during those years gets taxed at today's lower rate instead of tomorrow's — and tomorrow's rate, once everything piles up, is probably higher.

Every year you don't convert, that traditional IRA balance keeps compounding. Which means bigger RMDs. Which means more taxable income at 75, 76, 77 — every single year — whether you need the money or not. You're not avoiding taxes by doing nothing. You're just deferring them to a time when you have less control over the amount and zero control over the timing.

The 22% Bracket Ceiling: Where to Stop

You don't want to convert so aggressively that you push yourself into a high bracket. There's a natural ceiling most tax-aware planners use: convert up to the top of the 22% federal bracket, then stop.

Why 22%? Because RMDs at 75 will almost certainly be taxed at 22% or higher once you add up all your income sources. Converting at 22% now is almost always a clear win over paying that same rate or worse later — with no flexibility. Converting into the 24% bracket can still make sense but needs more case-by-case thought. Converting into 32% or above is usually not worth it.

Here's what "filling the 22% bracket" might look like for a married couple filing jointly in 2026:

That's a lot of room in this example. In practice you'd probably convert less than the maximum each year — especially once IRMAA enters the picture. But the point is: most retirees have significantly more bracket headroom during the conversion window than they ever realized.

What Happens If You Don't Convert

Say you have $800,000 in a traditional IRA at retirement. You decide to do nothing. That balance grows at 6% for 10 years. It's now roughly $1.43 million.

At age 75, the IRS requires you to withdraw a minimum amount each year based on your life expectancy. The Uniform Lifetime Table factor at 75 is 24.6, so your first RMD is about $58,000. Fully taxable. Stacked on top of whatever Social Security and pension you're already drawing.

At 76 the balance is still growing. The divisor shrinks. The required withdrawal increases. By 80, RMDs from a healthy account can be $75,000–$100,000 per year — all taxable, all mandatory, whether you need the money or not. And if you don't spend it all, it just piles into your taxable brokerage and creates more taxable income in future years.

That's the trap. The Roth conversion window is how you defuse it — deliberately, at a rate you control, in years where your income is lower.

IRMAA: The Cliff Nobody Mentions Until It's Too Late

Here's where Roth conversion strategy gets genuinely complicated, and where most people get blindsided.

Medicare premiums are not flat. If your income exceeds certain thresholds, you pay an Income-Related Monthly Adjustment Amount — IRMAA — on top of your standard Part B and Part D premiums. It's a cliff, not a ramp. Cross a threshold by one dollar and you owe the surcharge on the full year's premium.

That $888 at the first tier is per person on Medicare. Married, both on Medicare, both pushed over the threshold: you're each paying it. That's $1,776 you didn't budget for because you converted $1 too many. And it stings for two years, because of the lookback.

The 2-Year Lookback Is the Part That Actually Bites People

IRMAA doesn't look at this year's income. It looks at your income from two years ago. Your Medicare premiums at age 65 are based on what you earned at age 63. Your premiums at 66 are based on age 64 income. And so on.

This means the danger years don't start when you sign up for Medicare. They start at age 63. A large Roth conversion at 63 can spike your IRMAA surcharge the first year you're on Medicare — even though you weren't on Medicare when you did it. Most people find out when they get that first premium bill and it's mysteriously $74 per month higher than they expected.

The practical approach from age 63 on: find your IRMAA-safe conversion limit — the most you can convert without crossing a threshold — and treat that as your ceiling. You may leave some bracket room on the table. That's fine. You're avoiding a penalty that has nothing to do with your income tax rate and everything to do with a cliff you can't see until you've already fallen off it.

How to Actually Pay the Tax Bill

This is where people make a mistake that quietly undermines the whole strategy.

When you call your brokerage and initiate a Roth conversion, they'll ask whether you want to withhold taxes from the transfer. The correct answer is usually no. Pay the tax from your taxable brokerage or savings account — not from the conversion itself.

Here's why it matters. Say you convert $50,000 and the tax bill is $11,000. If you pay that $11,000 from a taxable account, the full $50,000 lands in the Roth and compounds tax-free from day one. That's the whole point. If instead you withhold $11,000 from the conversion, only $39,000 makes it into the Roth. You've paid the tax with pre-tax dollars that never got Roth treatment. That missing $11,000 compounds for decades. It's not a rounding error — it's a real and permanent drag on the strategy's value.

Quarterly Estimated Payments

Since you're retired with no employer withholding, you'll likely need to make quarterly estimated tax payments to cover conversion taxes throughout the year. The IRS wants its money in the year you earn it — not all at once next April. Form 1040-ES is how you handle this. If you skip it and pay the full bill at filing, you may owe an underpayment penalty on top. Your tax preparer can help you size the quarterly payments correctly for conversion years.

What the CrankyEarl Calculator Shows You

The Roth Conversion tab in the calculator runs through your conversion window year by year. For each year between retirement and age 74, it shows:

• Your projected traditional IRA balance, growing at your configured post-retirement return rate
• How much bracket room you have before hitting the top of the 22% federal bracket — calculated against your actual income sources including Social Security, pension, interest, and capital gains
• The suggested conversion amount to fill that bracket room, capped by your available balance
• The estimated tax cost of that conversion using your actual tax settings
• Your IRMAA-safe conversion limit for years from age 63 onward — the most you can convert without crossing a Medicare surcharge threshold
• An estimated net benefit comparing the tax cost of converting now against the estimated RMD tax burden at 75 if you don't

The net benefit number is directional, not a guarantee. It compares conversion cost against your first RMD's estimated tax — it doesn't model every future RMD after 75 or the full compounding value of Roth's tax-free growth, both of which make the case for converting even stronger. Treat it as a signal. The year-by-year table is the more actionable output — it shows you where the room is, where IRMAA applies, and what each year of converting actually costs you.

The Honest Limits of This Analysis

The calculator shows you the landscape. It doesn't replace a CPA. A few things that could affect your actual decision:

• State taxes. Some states tax Roth conversions, some don't. A high state income tax rate changes the effective cost of converting and could shift the math.
• Future tax rate changes. Nobody knows what federal brackets look like in 10 years. Converting now locks in today's known rate — which is itself an argument in favor of converting, but it's a judgment call, not a calculation.
• Estate planning. Heirs inherit Roth accounts income-tax-free. If leaving a tax-efficient legacy matters to you, that's a real benefit the net benefit number doesn't capture.
• IRMAA on both spouses. The calculator flags years where you're at risk, but the full two-person surcharge impact is something to work through with a tax advisor in those specific years.

None of this is an argument against converting. It's an argument for going in with accurate numbers and not winging it.

The Short Version

You have a window between when you retire and when RMDs start at 75. During that window, your income is probably lower than it will ever be again in retirement. Your tax brackets have room. The IRS is going to get paid on your traditional IRA eventually — the only question is at what rate and on whose schedule.

A Roth conversion lets you answer that yourself. Pay a known rate now, on an amount you control, in a year you choose. Stop at the top of the 22% bracket. Watch your IRMAA thresholds from age 63 onward. Pay the tax bill from outside money. Repeat each year until the window closes at 75.

It's not complicated. It's just something most people never think about until the RMDs start arriving and the options are gone.