Roth conversion calculator.

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How we calculate this

Both paths grow the exact same principal at the exact same rate — so the whole comparison comes down to one thing: which tax rate applies when the money finally comes out.

That's why the break-even is a rate, not a year: convert wins exactly when your future rate ends up above your current rate — regardless of how much you convert, how fast it grows, or how many years it has. Growth and years apply to both sides of the comparison equally, so they cancel out of the answer entirely; only the tax rates decide it, from day one. If you expect a lower bracket in retirement (common, since many people's income drops, which is also the premise behind the 4% rule's own tax assumptions), conversion usually costs you. If you expect a higher bracket — a big pension, large RMDs pushing you into a higher bracket later, filing single after a spouse — conversion usually pays off.

Does it matter how you pay the conversion tax?

A little, yes — enough that the calculator above lets you pick. Pay the tax bill straight from the conversion, and only the after-tax amount ever lands in the Roth: that's the "Convert" line in the box above, Future value × (1 − Rate now). Pay it from savings on the side, and the full converted amount grows tax-free instead.

That sounds like it should simply win by the whole tax bill's future value — but a fair comparison has to charge for what that outside money gives up by being spent early. The catch is that money isn't like the IRA: it's already been taxed once, so left alone, only its future growth would ever be taxed again, never its principal. Spending principal that was never going to be taxed anyway, to eliminate tax on money that otherwise would be taxed in full, is a good trade — and working through both sides of the ledger, it comes out to:

That extra term is the real, structural edge of paying from outside cash — it's exactly zero if there's no growth or either tax rate is zero, and it grows with time and with both rates, but it's usually a modest bonus on top of the main effect (which rate is higher), not the main event. It's part of why advisors generally recommend paying the tax from outside cash when you have it — not only because more money then compounds tax-free, but because the money you're spending on tax was never going to be fully taxed to begin with. One simplification worth flagging: this assumes that outside account has no gains sitting in it yet when you tap it — a real account you've held for a while may owe some tax at that moment too, which would eat into the edge above.

Frequently asked questions

When does a Roth conversion actually pay off?

A Roth conversion pays off when the tax rate you pay today is lower than the rate you'd pay later on withdrawals. If your rate is the same now and later, it's roughly a wash — the conversion only wins if you can pay the tax bill from outside savings, because that moves more after-tax dollars into the tax-free Roth.

Should I pay the Roth conversion tax from the IRA or from savings?

It matters more than most calculators admit. Paying the tax from the conversion itself shrinks the amount that lands in the Roth. Paying from outside savings (like a brokerage account) lets the full converted amount grow tax-free — and at equal tax rates, that difference alone can flip a losing conversion into a winning one. Toggle "Pay the conversion tax from" above to see it with your own numbers.

How much should I convert each year?

A common strategy is bracket filling: convert just enough each year to "fill up" your current tax bracket without tipping into the next one. The years between retirement and required minimum distributions (RMDs) — when your income is temporarily low — are usually the best window.

Do Roth conversions affect Medicare IRMAA premiums?

Yes. Converted amounts count as income in the year of conversion and raise your modified adjusted gross income (MAGI), which can trigger higher Medicare Part B and D premiums (IRMAA) two years later. Large conversions should be weighed against the IRMAA brackets as well as the tax brackets — this calculator doesn't model IRMAA (see the Assumptions box above); Runway's full planner does.