Compare a multi-year Roth conversion policy with doing no conversion. The model follows taxes, Medicare income-related premiums, required distributions, spending, and all three account types so the comparison ends in projected after-tax wealth rather than gross balances alone.
A Roth conversion moves eligible pre-tax retirement money into Roth savings. The taxable portion is generally included in ordinary income for the conversion year. Paying tax sooner may reduce later taxable withdrawals and required minimum distributions, but the early tax cost, other income, Social Security taxation, Medicare premiums, state tax, and the source used to pay tax can change whether the conversion improves projected after-tax wealth.
This calculator projects one household year by year from the starting tax year through the planning age. Every selected conversion policy receives its own automatically generated no-conversion baseline with the same starting balances, income, spending, returns, and horizon. That matched baseline is the reference for the advantage, break-even, lifetime-tax, RMD, and ending-wealth results.
Within each year the model takes any RMD first, funds spending with any needed Traditional withdrawal, resolves the entered conversion policy, calculates ordinary federal and estimated state tax, applies Medicare IRMAA from the two-year MAGI lookback, finishes funding spending and taxes, and then grows the remaining balances. This order prevents an RMD from being treated as a Roth conversion and limits only discretionary bracket-fill conversions to the selected taxable-income ceiling.
Tests each annual real conversion amount across each eligible start age and continues that amount through the common conversion end age. Feasible plans rank by after-tax wealth at the planning age, with lifetime tax and total converted used only to break ties.
After required spending is funded, solves the annual conversion that approaches the top of the selected 10%, 12%, 22%, 24%, 32%, or 35% federal bracket—or a custom taxable-income ceiling—after deductions and taxable Social Security are recalculated. A required Traditional withdrawal can put taxable income above that ceiling.
Attempts the entered today’s-dollar amount in each year of the conversion window, limited by available eligible pre-tax money after any RMD.
Projects the household without voluntary conversions. Use it alone to inspect the baseline or beside other scenarios to compare different assumptions.
Hypothetical example: an owner born in 1964 starts in 2026 with $1.5 million pre-tax, $150,000 Roth, and $300,000 taxable. The household retires at 65, plans through 90, receives $20,000 of other retirement income and $36,000 of Social Security from 70, spends $80,000 per year in today’s dollars, and tests conversions from 65 through 70.
| Result to inspect | What to look for | Why it matters |
|---|---|---|
| Best tested map | The highlighted amount/start-age pair and the nearby cells | A broad region of similar results is less sensitive to a small input change than a single isolated high cell. |
| Income and taxes | Whether conversions fill low-income retirement years, make more Social Security taxable, or trigger IRMAA two years later | The nominal bracket alone does not capture every cost of additional MAGI. |
| Account mix and RMD | How much earlier conversion reduces later pre-tax balances and the first RMD | Moving money to Roth changes both the timing of tax and the source of later spending. |
| After-tax advantage | Whether and when the strategy recovers its early tax cost and remains ahead | Ending gross balances can look better while spendable after-tax wealth is worse. |
| Scenario comparison | Repeat with a later Social Security start, a different state move age, or a lower return | Scenarios expose which assumptions, rather than the chosen policy alone, drive the result. |
The correct reading is not “the highlighted cell is what this household should convert.” It is “among the displayed candidates, this cell produced the highest modeled after-tax wealth while meeting spending under these assumptions.” Tax returns, account eligibility, cash availability, and current law still need separate review.
The model begins with published 2026 federal brackets, deductions, Medicare premiums, and IRMAA thresholds. It raises indexed values in unpublished future years with the entered inflation rate while leaving non-indexed Social Security thresholds unchanged. The $500,000 single/$750,000 joint top IRMAA threshold stays frozen through 2027, then receives its separate 2028 inflation base and statutory $1,000 rounding. Congress, the IRS, CMS, and SSA can change rules and amounts, and temporary provisions do not become permanent merely because the projection continues.
Each year applies one state transition: RMD, spending-driven taxable withdrawal and conversion-policy resolution, tax and IRMAA, remaining spending funding, then growth. Real transactions happen throughout a year, withholding and estimated payments have due dates, RMD timing can differ, and markets do not deliver one steady annual return. The model floors accounts at zero and records unmet spending rather than borrowing or inventing cash.
Married filing jointly can include a spouse’s age, Social Security, deduction, Medicare enrollment age, and covered Part B/Part D components, but only the named owner’s pre-tax retirement account is converted or receives RMDs. The model assumes all Traditional money is untaxed and does not model nondeductible basis or the Form 8606 pro-rata rule.
Sources reviewed August 2026. These official sources explain the rules used to seed the planning model; they do not endorse this calculator or its assumptions.
