Roth Conversions: Paying Tax Now to Take It Out Tax-Free Later

A Roth conversion moves money from a traditional 401(k) or IRA into a Roth account, taxing it as ordinary income now in exchange for tax-free growth and withdrawals later. Nothing is bought, sold, or added. You are choosing to pay a tax bill early, at a rate you know, rather than late, at a rate you do not. It is the most useful tool in the traditional vs Roth toolkit, and also the one most often described badly.

I put this off for two years because voluntarily writing a check to the IRS felt like the opposite of everything I had learned about retirement saving. It is not. It is the same decision I had already made every time I chose pre-tax over Roth at work, just made in reverse, later, with better information about my actual income.

What actually happens when you convert

The converted amount is added to your taxable income for that year and taxed as ordinary income, and the money then sits in a Roth where it grows tax-free¹. There is no early-withdrawal penalty on a conversion itself at any age, because the money is not leaving the retirement system.

The mechanics are usually simple: your custodian moves the money from the traditional account to a Roth account, and you get a form at tax time reporting the amount. What matters is what happens to your return. If your other income for the year is $30,000 and you convert $20,000, the IRS sees $50,000 of income. That is why the size of the conversion, not just the decision to convert, is the real question.

Withdrawals from the traditional account would have been taxed as ordinary income eventually anyway². A conversion just chooses the year.

Why early retirement is the classic window

The years after your paycheck stops and before Social Security and required minimum distributions start are usually the lowest-income years of your adult life, which makes them the cheapest years to move money. Once you are collecting Social Security at 67 and taking required withdrawals at 73, both land on your tax return whether you want the money or not³.

Think of the traditional balance as a bill you have deferred. Left alone, it keeps growing, and at 73 the IRS begins telling you how much of it you must withdraw and pay tax on each year. Converting during the quiet window shrinks that future bill, and it does so at a bracket you may never see again. This is also why people who retire at 62 and delay claiming, the approach discussed in when to claim Social Security, often have the most room to work with.

Other years worth watching: a year of unemployment, a year with a large business loss, or the year before a spouse’s benefit starts. Any year your income drops is a year conversions get cheaper.

The traps that catch people

Three things turn a sensible conversion into an expensive one: bracket spillover, the Medicare surcharge, and the pro-rata rule. Each is avoidable if you know it is there.

• Bracket spillover. Only the part of the conversion that rises above a bracket threshold is taxed at the higher rate, so this is not a cliff, but converting far more than you planned in one year is how people end up paying a top-bracket rate on money they could have moved slowly.
• The IRMAA cliff. Medicare’s income-related surcharge looks at your income from two years prior, and it genuinely is a cliff: a dollar over a threshold moves you into the whole next tier of Part B and Part D premiums⁴. We cover the thresholds and appeals in Medicare’s income surcharge.
• The pro-rata rule. If you hold any non-deductible (after-tax) money in a traditional IRA, you cannot convert only that portion. The IRS treats all of your traditional IRA balances as one pot and taxes the conversion in proportion, which surprises people attempting a backdoor Roth while an old rollover IRA sits in the background. See IRA accounts explained for how those balances interact.

Two more, smaller but real. Conversions can raise the share of your Social Security benefit that is taxable, covered in taxes in retirement. And state income tax applies too, which is why some people convert after a move.

The five-year rules, plural

A Roth IRA needs five years of life before earnings come out tax-free, and each conversion starts its own separate five-year clock for penalty purposes¹. People conflate these two rules constantly, so it is worth separating them.

The first is about the account: open a Roth IRA, wait five tax years, and once you are also 59½ the earnings are tax-free. The second is about the conversion: pull converted money back out within five years while you are under 59½ and a 10% penalty can apply, despite the tax already paid. Above 59½ that second rule largely stops mattering.

The practical takeaway is unglamorous. Convert money you can leave alone. If a sum is earmarked for a roof, a car, or a gap year of spending, it does not belong in a conversion.

Deciding how much, and when not to bother

Most people who convert well do it in annual slices sized to a target, not in one large move, and they reassess every year. The common target is filling a bracket: converting just enough to reach the top of your current tax bracket without spilling into the next, adjusted downward if an IRMAA threshold sits lower.

Conversions cannot be undone. Recharacterization was removed, so there is no do-over if December brings income you forgot about, which is another argument for slices and for waiting until late in the year when your income is nearly known. Pay the tax from outside the account, and see retirement withdrawal strategies for how conversions fit alongside your ordinary drawdown.

Converting is the wrong move when your tax rate today is the same or higher than it will ever be again, when paying the tax means selling something you would rather keep, when you will need the money inside five years, or when you plan to leave the account to a charity, which pays no income tax on it anyway. Heirs are a genuine argument in the other direction: under the rules in inherited retirement accounts, a traditional account left to adult children often lands on their return during their highest-earning decade.

This is general information rather than personalized tax advice, and investments can lose value in a Roth exactly as they can anywhere else⁵. The official figures live at IRS.gov and Medicare.gov, they change every year, and a one-page projection of your bracket and required withdrawals at 75, with and without conversions, is a fair thing to ask a fiduciary advisor or tax professional for. For the wider picture, start at retirement planning.