Roth Conversion Calculator
A Roth conversion moves money from a traditional IRA to a Roth IRA, paying income tax now in exchange for tax-free growth and withdrawals later. This calculator prices a conversion the way your return will: the bracket, plus the Social Security it makes taxable, the dividends it pushes out of the 0% rate, the ACA premium credit it costs, and the Medicare premiums it sets two years on. Then it draws the whole curve, so you can see where the next dollar gets dearer, and how long tax-free growth takes to break even.
What Drives a Roth Conversion
The core question is simple: Is my tax rate higher today or in retirement? If you expect a higher rate in retirement (due to RMDs, pension income, or Social Security), paying tax now costs less than paying it later. If your retirement rate will be lower, the conversion costs more than it saves.
The real comparison is marginal rate today vs. average rate in retirement. Today’s conversion is taxed at your current marginal rate. But in retirement, the avoided withdrawal fills brackets from the bottom — so the relevant comparison is the average rate on that withdrawal, not the marginal rate.
Three costs hide outside the bracket table. If you collect Social Security, each converted dollar can make up to 85 cents of benefits taxable too, so a 10% bracket costs 18.5% and a 12% bracket 22.2% until 85% of your benefits are taxable. If you buy health insurance on the ACA marketplace, every dollar of income gives back premium credit, and from 2026 one dollar past 400% of the poverty line gives back all of it. And a conversion that pushes your MAGI over a Medicare IRMAA threshold raises both spouses’ Part B and D premiums two years later, by about $2,300 a year for a couple at the first tier. This calculator prices each of them, separately, and shows the dollar where each one starts.
Partial conversions. A conversion sized to fill the current bracket stops short of the next one’s rate, and one sized below an IRMAA threshold stops short of the surcharge.