Estimate the federal tax cost of converting traditional IRA or 401(k) money to a Roth. See how much room is left in your current tax bracket, and whether a conversion would cross an IRMAA Medicare surcharge tier.
A Roth conversion moves money from a pre-tax account — a traditional IRA or 401(k) — into a Roth account. Because the original contributions were never taxed, the amount you convert is added to your taxable income for that year and taxed at ordinary income rates. In exchange, the money grows tax-free afterward and qualified withdrawals in retirement are not taxed.
The calculator above stacks your conversion on top of your other income and applies the 2026 federal brackets to estimate the additional tax. The "effective rate" is the total conversion tax divided by the amount converted — it's usually lower than your top marginal rate because the conversion fills the lower brackets first.
Many people convert just enough to "fill" their current tax bracket without spilling into the next one. The headroom figure above shows how much room is left before your income reaches the top of your current bracket. Converting beyond that point means the excess is taxed at the next rate up — which is why the calculator flags when a conversion crosses a bracket.
If you're near or over 63, a Roth conversion deserves extra care. Medicare sets your Part B and Part D premiums using your modified adjusted gross income from two years prior. A large conversion can push that income across an IRMAA threshold and raise your premiums for a future year. The calculator flags when your post-conversion income crosses a tier so the surcharge doesn't catch you by surprise.
A common window is the gap between leaving work and starting Social Security and required minimum distributions — often the early retirement years, when income may be low and there's room in the lower brackets. Converting during those years can reduce the size of future RMDs. Whether it makes sense depends on your whole picture: current and future brackets, IRMAA exposure, state taxes, and how long the money will grow. This tool surfaces the numbers; a licensed tax professional or fee-only advisor can help you decide.