Is a Roth Conversion Worth It? The Math, Honestly
What a Roth conversion actually does
A Roth conversion moves money from a pre-tax account (a traditional IRA or 401(k)) into a Roth IRA. The converted amount is added to your taxable income this year, so you pay ordinary income tax on it now. In exchange, that money — and all its future growth — becomes tax-free forever, with no required minimum distributions during your lifetime.
The entire question is whether prepaying the tax is a good trade. If tax rates (yours or the country's) will be higher when you would otherwise withdraw, you win by locking in today's lower rate. If your rate will be lower later — say you drop from a high-earning career into a modest retirement — converting means you volunteered to pay more tax than you had to.
The one comparison that decides it
Strip away the noise and a conversion comes down to rate now versus rate later. Everything else is a detail that nudges those two numbers. The classic winning setup is a gap year: you have retired or taken a sabbatical, your income has dropped, but Social Security and required minimum distributions have not started yet. Your bracket is temporarily low — often 10 or 12 percent — while your future bracket, once RMDs and Social Security stack up, could be 22 percent or higher.
To find your personal breakeven — the future tax rate at which converting stops being worth it — run your numbers through our Roth conversion breakeven calculator. It compares the tax cost today against the projected tax saved later and tells you the crossover point in plain dollars.
A worked example: the gap-year conversion
Consider Marcus, 63, retired early, married filing jointly, with 40,000 dollars of taxable income this year from a small pension. After the 30,000 dollar 2025 standard deduction, his taxable income is modest and he sits comfortably in the 12 percent bracket with room to spare before the 22 percent bracket. He has 500,000 dollars in a traditional IRA that will trigger large RMDs at 73, likely taxed at 22 percent or more.
| Scenario | Amount converted | Tax rate paid | Tax cost |
|---|---|---|---|
| Convert now (gap year) | $40,000 | 12% | $4,800 |
| Leave it, withdraw later | $40,000 | 22% | $8,800 |
| Savings from converting | 10 pts | $4,000 |
By converting 40,000 dollars this year at 12 percent, Marcus pays 4,800 dollars in tax now instead of 8,800 dollars later — a 4,000 dollar saving on this slice alone, before you even count decades of tax-free growth. The trick is not converting so much that he spills into the 22 percent bracket himself. That is exactly the line the tax bracket fill-up planner helps you draw — it tells you how many dollars you can convert to fill up your current bracket without tipping into the next one.
The details that quietly break the math
Three things turn a good conversion into a bad one:
1. Paying the tax from the IRA itself. A conversion works best when you pay the tax bill from a separate taxable account. If you have to pull the tax money out of the IRA, you shrink the balance that grows tax-free and — if you are under 59 and a half — may owe a 10 percent penalty on the withdrawn portion. Pay the tax from cash on the side.
2. Ignoring bracket and surcharge cliffs. A large conversion can push you past thresholds that cost real money: the 22-to-24 percent bracket line, the Net Investment Income Tax threshold, higher Medicare Part B and D premiums (IRMAA), and taxation of Social Security benefits. Convert in measured annual slices, not one big lump.
3. A shorter horizon than you think. The tax-free growth needs time to outrun the upfront tax cost. The breakeven calculator shows how many years it takes for the conversion to come out ahead — if you expect to spend the money before then, converting may not pay.
One more nuance worth naming: your future rate is not only about your personal income. Statutory tax rates themselves can rise. Several of the current brackets are scheduled to revert to higher pre-2018 levels unless Congress extends them, which strengthens the case for locking in today's rate while it is known. That is a policy bet, not a certainty, so weigh it alongside your own income trajectory rather than treating it as the whole argument.
Finally, a conversion is not all-or-nothing across your lifetime. Many people run a multi-year conversion ladder, moving a measured slice each year through their low-income window so no single year spills into a higher bracket or trips a surcharge cliff. Re-run the breakeven each year as your income and the balance change.
Frequently asked questions
When is a Roth conversion clearly worth it?
When your current tax rate is lower than your expected future rate, you can pay the conversion tax from outside the IRA, and you have enough years for tax-free growth to compound. Low-income gap years before Social Security and required minimum distributions begin are the textbook opportunity.
When is a Roth conversion a mistake?
When your future tax rate will be lower than today's — for example if you are at peak earnings now and expect a modest retirement — or when you must pay the conversion tax out of the IRA itself, which shrinks the tax-free balance and can trigger an early-withdrawal penalty.
How much should I convert in one year?
Generally only enough to fill up your current tax bracket without spilling into the next one. Converting a lump sum can push you into a higher bracket and trigger cliffs like the Net Investment Income Tax and higher Medicare premiums. A bracket fill-up planner shows the exact dollar ceiling.
Do I have to pay tax on a Roth conversion?
Yes. The converted amount is added to your taxable income for the year and taxed at ordinary income rates. That upfront tax is the entire cost of the trade — you pay it now so that all future growth and qualified withdrawals are tax-free.
What is the five-year rule on conversions?
Each Roth conversion has its own five-year clock. To withdraw the converted principal penalty-free before age 59 and a half, five tax years must pass since that conversion. After 59 and a half the rule is generally moot for the converted amount, but plan conversions with the timeline in mind.
Can a Roth conversion raise my Medicare premiums?
Yes. Conversions increase your modified adjusted gross income, which Medicare uses two years later to set IRMAA surcharges on Part B and Part D. A large conversion at age 63 or 64 can raise premiums at 65 or 66, so size conversions with IRMAA thresholds in view.
🧾 Handle your taxes
File your taxes online →FileYourTaxes — IRS-authorized e-file · Built for self-employed & 1099 filersMatch with a fiduciary advisor → · Free Match
SmartAsset — Free advisor matching · Fiduciary only · No obligation · 2 minutes
Investor Sam may earn a commission if you sign up. This does not affect our analysis.