Trust matters more than a bigger number. This page explains, in plain English, exactly what our engine calculates, so you can check our reasoning with your CPA or advisor.
When you take an extra dollar from an IRA in retirement, three things can happen at once: the dollar itself is taxed at your bracket rate, more of your Social Security can become taxable (often called the "tax torpedo"), and above certain incomes the new senior bonus deduction phases out at 6 cents per dollar in this model. UNCONFIRMED: that 6% phase-out rate is CRS-sourced (OBBBA senior deduction), not an IRS-published 2026 table. We calculate the true cost of your next $10,000 of IRA income by running your full return twice and comparing, that's the big percentage on your results page.
We apply the federal provisional-income formula: depending on your income, 0%, up to 50%, or up to 85% of your benefits become taxable. Tax-exempt interest counts in this formula, which surprises many people.
Medicare charges income-based premium surcharges when your modified adjusted gross income crosses set thresholds ($218,000 / $274,000 / $342,000 / $410,000 / $750,000 for joint filers in our 2026 model; roughly half for single filers). Two things make these dangerous: they are cliffs, $1 over a line triggers the full surcharge for the year, per spouse on Medicare, and they look back two years, so this year's decisions set premiums two years from now. We show your distance to the next threshold and the dollar cost of crossing it.
Pre-tax retirement accounts require withdrawals starting at age 73 (or 75 if you were born in 1960 or later). UNCONFIRMED: the RMD age for birth year 1959 is not treated as settled in this product; the model uses age 73, the same as 1951–1958. We project your balance forward at an assumed 7% annual growth and estimate your first required withdrawal using the IRS uniform lifetime table. That forced, fully-taxable income is the deadline most planning works against.
For your numbers, we solve for the conversion amounts that fill your current tax bracket to its top, and the amounts that reach each Medicare threshold. Those are natural stops to compare with doing nothing, not a recommended conversion amount. Bring the comparison to a CPA or fiduciary.
We simulate your household year-by-year to age 90 under a do-nothing path and under annual Roth conversion plans from $10,000 to $250,000 per year, counting federal taxes and Medicare surcharges along the way, discounted to today's dollars at 5%. If no conversion plan beats doing nothing, we say so, the honest answer is sometimes "hold steady."