Where Will the Tax Come From on a Roth Conversion?

Most people pick the strategy and skip the question that decides it

You’ve probably read the case for a Roth conversion. Move money out of a traditional IRA, pay the tax now, and the money grows tax-free from there. Fine. But here’s the question almost nobody asks first: when that tax bill comes due, where is the cash actually coming from?

Knowing how to fund the tax bill is one part of the decision. The other part is knowing when to convert, and there is a window most people do not notice until it is half gone. See The Roth Conversion Window Opens Earlier Than You Think.

It sounds like a small detail. It isn’t. It’s the difference between a conversion that works and one that quietly underperforms for the next twenty years.

There’s no required withholding on a conversion, which means you get to decide. That’s good news, as long as you decide on purpose.

Where does the money to pay the tax actually come from?

You have two real options.

One, you pay the tax from outside the IRA. You convert, say, $100,000, and you cover the resulting tax bill with money you already have in a savings or brokerage account. The full $100,000 lands in the Roth.

Two, you pay the tax from inside the IRA. You have the custodian hold back enough to cover the bill, or you pull a little extra to cover it. Now only part of the money makes it into the Roth, and the rest goes straight to the IRS.

I’ll keep it plain. Option one is almost always the better answer. Here’s why option two costs you more than it looks like.

Pay tax on the seed, not the harvest

There’s an old way to think about this. You can pay tax on the seed or on the harvest. The seed is the smaller number, the amount you convert today. The harvest is everything that money grows into over the next two or three decades. A conversion is a deliberate choice to pay tax on the seed now so the harvest comes out tax-free later.

That only works if you actually plant the whole seed. Every dollar you pull from the IRA to pay the tax is a dollar that never gets planted in the Roth. It never grows tax-free, and you’ve spent it on taxes anyway.

Picture the round numbers. Convert $100,000, and say your blended rate on that income works out to roughly 22%, about $22,000 in tax. (Illustrative and hypothetical, your real rate depends on your full income picture for the year.) Pay the $22,000 from outside money and the entire $100,000 is in the Roth, compounding for you. Pay it from the IRA and only $78,000 makes the trip. That missing $22,000 doesn’t just vanish for a year. It’s gone from the tax-advantaged side of your plan for good, along with everything it would have grown into. Over twenty-plus years, that’s the most expensive way to settle a tax bill you’ll find.

The under-59½ trap that catches people every year

This is the part that makes financial advisors go pale, and it happens more than it should.

If you’re under 59½ and you let the custodian withhold the tax from the conversion, those withheld dollars are not treated as converted. The IRS treats them as a regular early withdrawal from your IRA. The withheld amount gets hit with the 10% early distribution penalty, on top of the income tax you already owed.

You set out to pay your tax, and the act of paying it created a brand-new tax. On our $22,000 example, that’s roughly another $2,200 to the IRS for nothing. People tend to find this out after the fact, on a form, when it’s too late to undo. And there’s no undo anymore. Recharacterization, the old reverse-the-conversion escape hatch, has been gone since 2018. Once you convert, it’s permanent.

For almost everyone under 59½, paying the tax from outside the account is the better move by a wide margin. Could the penalty ever be worth it, for someone with enough already sitting in tax-free accounts? Run the numbers and you’ll see. If converting and eating the penalty changes your lifetime picture by a meaningful amount, it’s a real conversation. If it barely registers, the answer is no. The math tells you which one you’re looking at.

A conversion can change what you owe in April, too

One more piece people miss. Adding a conversion to your income can leave you short on what you’ve paid in during the year, which can mean an underpayment at tax time. It can also nudge your income high enough to raise your Medicare premiums two years down the road, a surcharge called IRMAA. None of that is a reason not to convert. It’s a reason to size the conversion and plan the tax payment before you pull the trigger, not after.

This is also why a conversion never happens in a vacuum. It bumps against your required minimum distributions later, your Social Security taxation, and the rest of the structure. Those forces feed each other regardless of where tax rates go.

Why having the outside cash changes the whole plan

Here’s where most planning stops, and where ours doesn’t.

Traditional advice treats the outside money you spend on the tax as money that’s simply gone. Pure cost. And if a Roth conversion were only ever a gift you leave behind, that would be the end of it.

It isn’t, and this is the part worth slowing down for. There’s a way to buy guaranteed lifetime income at what amounts to a wholesale price, by setting it up years before you need it instead of at retail the day you retire. Get to it early enough and Roth money doesn’t have to sit and wait to become an inheritance. It can be turned into income you actually spend. That changes the math on paying the tax from outside money, because the converted balance isn’t frozen for the next generation. It’s working for you while you’re alive.

The catch is timing. You need to be early, and you need the outside cash ready when the low-tax window opens. That’s the whole reason we push to get in front of people sooner rather than later.

The real answer to every one of these questions

You’ve probably noticed that every question on this page lands in the same place. Pay from outside or inside? How big should the conversion be? Is the penalty ever worth it? Should you convert at all? The answer to all of them is the same: run the numbers, on software you trust, before you move a dollar.

The numbers don’t make the decision for you. They show you the size of what’s at stake, and then you decide. If the math says a conversion changes your lifetime picture by a hundred thousand dollars, that’s worth a hard look. If it says twenty-five thousand, maybe, and that’s your call. If it barely moves the needle, the decision just got easy. Either way, you’re deciding with the real figures in front of you instead of a rule of thumb.

That’s why we don’t lean on the calculators floating around online. Most of them will lead you wrong, even by accident, because they can’t see your whole picture, your other income, your spouse, your timeline, the way one piece sets off the next. We run your real numbers on what we believe is the most accurate conversion engine in the industry, and part of the job is showing you exactly where the tax should come from and whether the move clears the bar for you.

And here’s the part that should make looking easy. Running the numbers is free and reversible. The conversion isn’t, there’s no recharacterization anymore. It never hurts to look, but it can hurt to act without looking. Sometimes the numbers say convert. Sometimes they say leave it alone, and we’ll tell you straight when they do.

Experience: Kurt H. Jackson has spent more than 16 years working directly with retirees and pre-retirees in Missouri, Nebraska, Kansas, Iowa, and Florida. After the dot-com crash in 2003, he started reverse-engineering the traditional save-and-withdraw model, and what he found changed everything about how he approaches retirement income. Before founding KJ Financial, he spent 20+ years as a Certified Mortgage Planner working with more than 1,000 clients.

Expertise: Kurt is a Retirement Lifestyle Architect and the creator of the Lifestyle-First Retirement Income Planning framework. He is Life and Health Insurance Licensed in MO (8035802), NE, KS, IA (NPN 14954049), and FL (W192044). His practice focuses exclusively on insurance-based, tax-optimized retirement income strategies including Protected Lifetime Income (PLI) design, Roth conversion planning, and the 6-Link Tax Cascade. He does not manage investments or sell securities.

Authoritativeness: Kurt founded KJ Financial and operates MaxMyRetirementIncome.com as a dedicated educational resource for retirees. His Lifestyle-First framework is built on peer-reviewed research from Wade Pfau, Morningstar, BlackRock, and EBRI. Every income figure published on this site is based on actual carrier quotes and current research, updated regularly.

Trustworthiness: KJ Financial is a compliance-first firm. All income figures are presented as illustrative and hypothetical. Kurt H. Jackson is not a securities broker, registered investment advisor, or CPA. Guarantees rely on the claims-paying ability of the issuing insurance company.

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