Understand the cliffs before you convert.
Short, plain-language explainers on the rules that make a Roth conversion more than a federal-tax calculation — the IRMAA two-year lookback, the two different 5-year rules, and the thresholds a conversion can quietly trip. Then run your own numbers in the calculator.
Start here
The IRMAA two-year lookback, explained
Medicare's income surcharge is a real cliff — one dollar over a tier raises your premium by a fixed annual amount — and it arrives on a two-year delay. Here's why a conversion today shows up on your Medicare bill two years from now, and what that means if you're 63 and planning ahead.
The two Roth 5-year rules (and why you can't undo a conversion)
Most calculators conflate them. There's a 5-year clock for tax-free earnings and a separate 5-year clock for penalty-free access to each conversion. Which one bites depends on your age — and since 2018 there's no take-backs.
The hidden cliffs: NIIT and Social Security taxability
A Roth conversion is ordinary income, but it can still pull a 3.8% surtax onto your other investment income and push more of your Social Security into the taxable column. Two thresholds most conversion calculators ignore.
See your own numbers
The Roth conversion cliff calculator maps the federal bracket, IRMAA tier, NIIT threshold, ACA cliff, and Social Security band against your projected income, and shows the largest conversion that clears every cliff. It runs entirely in your browser — nothing you enter leaves your device.
These guides are educational and not tax or investment advice. See our disclaimer.