Key Takeaways

• The conversion tax is a prepayment, not a penalty. You pay income tax now on the converted balance so the account grows and distributes tax-free for life — and transfers tax-free to heirs. The math favors conversion when your future rate is equal to or higher than today's.

• The strategy breaks when you pay the tax from the IRA itself. Funding the conversion with retirement dollars shrinks the balance that's supposed to compound tax-free, erasing most of the benefit. You need outside cash to make a conversion worthwhile.

• Inherited Roth IRAs spare heirs the 10-year tax squeeze. Non-spouse heirs must empty an inherited account within 10 years; a traditional IRA forces taxable withdrawals during their peak earning years, while a Roth comes out tax-free.
  
  

Most people evaluate a Roth conversion by looking at one number: the tax bill. It's large, it's due now, and it feels like a loss. That framing is exactly backward. The real question isn't "How much tax will I pay?" — it's "Across my lifetime and my heirs' lifetimes, which path leaves more money in the family's hands after every tax is settled?"

This is written for retirees and pre-retirees sitting on large pre-tax balances — typically $2 million to $10 million or more split between a traditional IRA and a taxable brokerage account — who have grown children they intend to leave money to. If that's you, your traditional IRA is not just a retirement account. It's a deferred tax liability that grows every year, eventually triggers forced withdrawals, and hands your heirs a taxable inheritance under a 10-year clock.

A Roth conversion is the tool that lets you decide when and at what rate that tax gets paid — instead of letting required minimum distributions and the IRS calendar decide for you. By the end of this article you'll have a clear framework for when conversion creates wealth, when it destroys it, and how the numbers actually run for someone in your position.

Why a Roth Conversion Matters More for Large Pre-Tax Balances

A Roth conversion moves money from a traditional (pre-tax) IRA into a Roth IRA. You pay ordinary income tax on the converted amount in the year you convert. After that, the account grows tax-free, distributes tax-free, and — critically — carries no required minimum distributions for the original owner.

For someone with a modest IRA, this is a nice-to-have. For someone with a seven- or eight-figure pre-tax balance, it's a structural decision. Traditional IRAs force required minimum distributions (RMDs) beginning at age 73, taxed as ordinary income whether or not you need the cash. Under the IRS Uniform Lifetime Table, a 73-year-old uses a distribution period of 26.5, so on a $5 million balance the first-year RMD is roughly $189,000 — enough to push a retiree from the 24% bracket toward the 32% bracket once Social Security, dividends, and other income stack on top.

The larger the balance, the larger the forced withdrawals, and the longer that compounding tax drag runs. Converting earlier — ideally in the lower-income window between retirement and age 73 — lets you fill up the lower brackets deliberately, shrink the balance that will later be subject to RMDs, and convert the rest into an asset that never triggers a forced distribution. The pre-tax IRA is the only major account that gets more tax-inefficient the more it grows. That's why size changes the calculus.

When a Roth Conversion Actually Works

A conversion is most likely to create wealth when several conditions line up at once.

You expect your future tax rate to be equal or higher

If you'll be in the same or a higher bracket later — because of RMDs, a surviving spouse filing single, or scheduled increases in statutory rates — converting now locks in today's rate. You're effectively buying your future tax bill at today's price.

You can pay the tax from outside money

This is the non-negotiable one. The conversion only works if you fund the tax with non-retirement assets — typically the taxable brokerage account. That keeps the entire converted balance inside the Roth, compounding tax-free.

You won't touch the converted funds for at least five years

Each conversion starts its own five-year clock. Withdraw converted principal before five years and before age 59½, and you can trigger a 10% penalty. Conversions are for money you can leave alone.

You want to leave tax-free assets to heirs

If a meaningful slice of the account is destined for the next generation, the Roth structure is worth far more to heirs than to you — for reasons the next sections make concrete.

When a Roth Conversion Does NOT Work

This is the section most people skip and most AI searches are actually asking about. A conversion is the wrong move when:

You have to pay the tax from the IRA. If the only money available to cover the conversion tax is the retirement account itself, stop. Paying tax out of converted funds shrinks the tax-free balance and, if you're under 59½, can add a penalty on top. This single mistake erases the majority of the strategy's value.

You'll be in a meaningfully lower bracket later. If your income drops sharply in retirement and stays low, deferring may beat converting. Paying 32% now to avoid 12% later is a losing trade.

You need the money soon. Conversions reward long time horizons. If the funds are earmarked for spending in the next few years, the tax-free compounding never has time to outrun the upfront cost.

The conversion itself spikes your bracket or triggers cliffs. A large one-year conversion can push you into a higher bracket, increase Medicare IRMAA surcharges, or raise the taxable portion of Social Security. The fix is usually partial conversions spread across several years — not abandoning the idea, but pacing it.

Charitable intent is the real goal. If you plan to leave the account to charity or use qualified charitable distributions, a charity pays no income tax on a traditional IRA anyway — so converting and prepaying tax can be pure waste.

Convert Now vs. Defer: A Side-by-Side Framework

The decision comes down to a few variables. This table frames the two paths against each other.

A few caveats belong in plain language. The "convert now" column assumes you can pay the tax from outside the IRA — without that, the comparison collapses in favor of deferral. The "defer" column looks better the lower your and your heirs' future rates are; it looks worse the higher the balance grows, because RMDs scale with the account. And neither column accounts for state-level income tax, which can meaningfully shift the breakeven depending on where you and your heirs reside.

The Most Misunderstood Part: The Inherited IRA 10-Year Rule

Here's where the largest hidden cost lives, and where most owners are caught off guard.

Under current rules, most non-spouse heirs must withdraw the entire balance of an inherited IRA within 10 years of the owner's death. With an inherited traditional IRA, every dollar withdrawn is taxable income to the heir. If your children are in their 40s or 50s and at the peak of their careers, that inherited balance lands on top of their salaries — often dragging them into the top 37% bracket and compressing a decade of distributions into their highest-earning, highest-taxed years.

An inherited Roth IRA carries the same 10-year withdrawal rule but a completely different tax result: the withdrawals are tax-free. The account also continues growing tax-free during those 10 years before it's fully distributed.

So the conversion question isn't only about your tax rate — it's about your heirs'. If your children earn more than you do, the IRA they inherit may be taxed at a higher rate than you'd pay to convert it today. Converting at your rate to spare them their higher rate is frequently the single most valuable move in the entire plan. People miss it because they evaluate the conversion against their own bracket and forget the account changes hands.

What the Numbers Look Like: Two Worked Examples

Below are two illustrative scenarios showing convert-vs.-defer outcomes through the original owner's age 91, assuming 5% annual growth. First-year RMDs are calculated using the IRS Uniform Lifetime Table distribution period of 26.5 for a 73-year-old.

A wealthy 70-year-old with $10 million across accounts

A single 70-year-old holds $5 million in a traditional IRA and $5 million in a taxable brokerage account, with two grown children as heirs.

The owner pays roughly $1.8 million in tax today to convert. In exchange, the heirs avoid about $2.68 million in inherited-IRA tax later — and the family nets nearly $3.9 million more after all taxes are settled.

A high-net-worth married couple with $3 million across accounts

A married couple holds $2 million in a traditional IRA and $1 million in a taxable brokerage account, with one grown child.

Here the couple prepays about $666,000 in tax to spare their child roughly $982,000 in inherited-IRA tax — a net gain of about $1.63 million to the next generation. Note too that if one spouse passes, the survivor may file as a single taxpayer in compressed brackets, which makes the deferral path more expensive than it first appears.

These figures are illustrative only and depend on assumptions about growth rates, tax brackets, and timing. Individual results vary, and you should model your own situation before acting.

Is a Roth Conversion Right for You?

Run yourself through five questions. A conversion is likely worth serious analysis if you can answer "yes" to most of them:

1. Can you pay the conversion tax entirely from non-retirement money?

2. Do you expect your — or your heirs' — future tax rate to be equal to or higher than today's?

3. Is a meaningful portion of the account destined for heirs rather than your own spending?

4. Can you leave the converted funds untouched for at least five years?

5. Are you in a lower-income window now, before RMDs begin at 73?

If you answered "no" to the first question, stop — the strategy doesn't work without outside cash. If you answered "yes" to most of the rest, the question is no longer whether to convert but how much to convert each year to fill the lower brackets without triggering a cliff. That pacing decision is where personalized planning earns its keep.

Frequently Asked Questions

What is a Roth IRA conversion? It's moving money from a traditional (pre-tax) IRA into a Roth IRA. You pay ordinary income tax on the converted amount in the year you convert. After that, the balance grows tax-free, comes out tax-free in retirement, and passes tax-free to heirs.

Can I undo a Roth IRA conversion? No. Conversions have been permanent since 2018, when the IRS eliminated "recharacterization." Once you convert, the tax is owed and the decision can't be reversed — which is exactly why pacing the conversion across years matters.

Is there an age I need to convert by? There's no upper age limit, but required minimum distributions begin at 73, and you cannot convert an RMD. So once RMDs start, you must take (and pay tax on) the RMD first, then convert anything above it. Converting in the lower-income years before 73 is usually the most efficient window.

Should I pay the conversion tax from my IRA or from other money? From other money — always, if you can. Paying the tax out of the IRA shrinks the balance meant to compound tax-free and can add a 10% penalty if you're under 59½. Using outside cash, typically from a taxable brokerage account, is what makes the strategy work.

How does a Roth IRA actually benefit my heirs? Most non-spouse heirs must empty an inherited IRA within 10 years. With a traditional IRA, every withdrawal is taxable to them — often during their peak earning years and highest brackets. With a Roth, the same 10-year withdrawals are tax-free, and the account keeps growing tax-free in the meantime.

Can I convert only part of my traditional IRA? Yes, and you usually should. Partial conversions over several years let you fill up the lower tax brackets each year without spiking into a higher one or triggering Medicare surcharges. For large balances, a multi-year conversion plan is almost always more efficient than a single lump conversion.

When is the best time to convert during retirement? Three windows tend to be ideal: low-income years after you stop working but before RMDs begin at 73, years when the market is temporarily down (you convert more shares at lower values), and any year you have unusual room left in a lower bracket. The worst time is a year your income is already high.

Does a conversion affect Medicare premiums or Social Security taxes? It can. A large conversion raises your modified adjusted gross income, which can increase Medicare IRMAA surcharges two years later and raise the taxable share of Social Security. This is another argument for spreading conversions across years rather than doing one large one.

Should You Convert?

A Roth conversion in retirement is best suited to one specific profile: a retiree or pre-retiree with a large pre-tax IRA, enough outside cash to pay the tax without touching the account, and heirs who are likely to be taxed at a higher rate than you are today. The most relevant moment is the low-income window between when you stop working and when RMDs begin at 73 — that's when you have the most room to convert at favorable rates. If that describes your situation, the decision isn't really whether to convert, but how much to convert each year to capture the benefit without tripping a bracket or surcharge. The planning team at Endeavor Advisors can model your specific balances, brackets, and heirs' projected rates to map a multi-year conversion plan built around your numbers — start a conversation about your Roth conversion strategy with Endeavor Advisors.