A Roth conversion is the deliberate act of moving money from a pre-tax account (a traditional IRA or an old 401(k)) into a Roth IRA. You voluntarily pay income tax on the converted amount this year, and in exchange all future growth and qualified withdrawals become tax-free. Done in the right year, it is one of the most powerful tools retirees and early-retirees have. Done carelessly, it can trigger surprise costs.
Why anyone would volunteer to pay tax early
The logic is pure arbitrage on tax rates: if your rate today is lower than your expected rate later, paying now is a bargain. The classic setups are low-income "gap" years:
- The years between retiring and starting Social Security or required minimum distributions (RMDs), when taxable income can be unusually low.
- A sabbatical, layoff, or a business's down year.
- Any year a market drop has temporarily shrunk your IRA — you convert the same shares while they are "on sale," so more of the recovery happens inside the Roth.
There is also a longevity angle: pre-tax balances eventually force RMDs, which can push retirees into higher brackets and raise Medicare premiums. Converting earlier shrinks the future RMD and the taxes that come with it. Roth IRAs themselves have no lifetime RMDs.
Check your bracket headroom →Use the calculator to see how much room is left in your current bracket before a conversion pushes you into the next one.How the tax is calculated
The converted amount is added to your ordinary income for the year and taxed at your marginal rates. The skill is "filling up a bracket": converting just enough to reach the top of your current bracket without spilling into the next. If you are single and your taxable income sits at $60,000, you might convert roughly up to the top of the 22% bracket, capturing cheap Roth space without jumping to 24%. Understanding marginal versus effective rates is essential here.
Always pay the conversion tax from outside the retirement account (from cash savings). Using the IRA itself to pay shrinks the amount that gets to grow tax-free and, if you are under 59½, can create an early-withdrawal penalty on the portion used for taxes.
Watch the ripple effects. A conversion raises your income for the year, which can increase Medicare Part B and D premiums two years later (the IRMAA surcharge), reduce ACA marketplace subsidies, and affect the taxation of Social Security. These second-order costs are why conversions are best sized carefully — often across several years rather than one big move.
The five-year rules
Roth conversions carry their own five-year clock: each converted amount generally must season for five years before the converted principal can be withdrawn penalty-free if you are under 59½. There is also a separate five-year rule for a Roth account's earnings to be qualified. These rules rarely bite retirees who leave the money alone, but they matter for early retirees planning to tap converted funds soon — plan the sequence deliberately.
Who should probably skip it
If you are in your peak-earning, high-bracket years, converting now usually means paying the highest rate you will ever face — the opposite of the goal. Conversions also make less sense if you expect to be in a much lower bracket in retirement anyway, or if you would have to raid the account to pay the tax. Because the interactions with Medicare, Social Security, and ACA subsidies are genuinely complex, a Roth conversion plan is a textbook case for professional advice before you pull the trigger.