Roth conversions explained: moving pre-tax money to tax-free

A Roth conversion is one of the most useful moves in retirement planning and one of the most misunderstood. The idea is simple: you move money from a pre-tax account (a Traditional IRA or 401(k)) into a Roth account, pay ordinary income tax on the amount you move this year, and in exchange that money — and all its future growth — becomes tax-free forever. You're voluntarily paying the tax now to escape it later. Whether that's smart depends entirely on your tax rate today versus the rate that money would face if you left it alone.

How a conversion works

You tell your custodian to convert some or all of a Traditional balance to Roth. The converted amount is added to your taxable income for the year, so you owe income tax on it at your marginal rate. There's no 10% early-withdrawal penalty on a conversion (unlike an actual withdrawal), and there are no income limits on who can convert — which is exactly what makes the 'backdoor Roth' work for high earners. The key is that you should pay the resulting tax from outside the account, so the full converted amount lands in the Roth to grow.

When conversions make the most sense

• Low-income years between retirement and RMD age, when you can fill up the low tax brackets cheaply.
• Early in retirement before claiming Social Security, keeping your taxable income temporarily low.
• After a market drop, when converting the same shares costs less tax — you move more shares per tax dollar.
• To shrink future RMDs that would otherwise stack on Social Security and push you into higher brackets and Medicare surcharges.
• To leave tax-free money to heirs, who must otherwise drain an inherited Traditional account (and pay income tax) within 10 years.

The bottom line

A Roth conversion trades a tax bill today for tax-free growth and withdrawals forever — a good deal when your current rate is lower than the rate that money would otherwise face. Low-income years, early retirement, and market dips are the prime windows, and shrinking future RMDs or leaving tax-free money to heirs are common motivations. Pay the tax from outside the account, watch the ripple effects on Social Security taxation, IRMAA, and ACA subsidies, and remember it's irreversible. For anything beyond a small conversion, a CPA or fee-only planner can model whether the timing is right for you.