“I'm 64 with $2M in an IRA. Is a Roth conversion still worth it?”

Probably — but not for the reason most articles give, and not by as much as most calculators claim. The honest answer requires a number nearly every free Roth tool computes incorrectly.

The window is real

Born in 1962, your RMDs start at 75. That's an eleven-year window where you control your own taxable income — especially if you haven't claimed Social Security yet. In those years you can deliberately fill a low bracket with converted dollars, pay tax at a rate you choose, and permanently remove that money from every future RMD.

The alternative is letting $2M compound to perhaps $3M by 75, then having the IRS pull roughly $120,000 out every year, on top of Social Security, at whatever bracket that lands you in.

The number everyone gets wrong

Here's where most Roth calculators mislead you. They compute your "available bracket headroom" as though you have no income — just Social Security, maybe not even that. Then they tell you you're in the 10% bracket with $24,800 of cheap room to convert into.

But you're retired. You're living on something. If you're spending $110,000 a year and pulling most of it from that IRA, those withdrawals are ordinary income — and they're already filling the very brackets the calculator just told you were empty. Your real marginal rate might be 22%, not 10%, and your real headroom a fraction of what you were shown.

This isn't a small error. It's the difference between a conversion that's clearly worth it and one that's roughly a wash.

What actually decides it

• Your real marginal rate during the window — measured against the income you actually generate, not a blank slate.
• IRMAA. A conversion inflates MAGI, and MAGI sets your Medicare premium two years later. Cross a threshold by a dollar and the surcharge is not prorated. A conversion that looks good on brackets alone can lose to the cliff.
• Who's left. If one of you dies, the survivor files single — same income, roughly half the brackets. That's the widow's penalty, and it's an argument for converting while you're both here.
• Your heirs' brackets. An inherited IRA now empties in ten years, often into your children's peak earning years.