Roth Conversion Ladder — Bridge Fund Calculator
Most Roth conversion ladder calculators assume the bridge money is already sitting in a taxable brokerage account. This one works backward from your future ladder to tell you how much to save each month, starting today, to have that tax money ready before you retire early.
Required monthly savings
to fully fund your tax-bill prefund without touching the IRA itself.
Each rung is a year's conversion tax bill. Bar length shows that rung's share of the total target.
A Roth conversion ladder lets early retirees move money from a Traditional IRA or 401(k) into a Roth IRA in controlled yearly chunks, paying income tax on each chunk at a low bracket instead of waiting until required minimum distributions force it at a higher one. The catch: each conversion has to sit in the Roth account for five years before it can be withdrawn penalty-free. That five-year wait is the "bridge" — and every year of it comes with a tax bill due immediately, whether or not the money is accessible yet.
Most Roth conversion ladder calculators start from the assumption that this bridge money — the cash to pay those tax bills — already exists in a taxable brokerage account. This calculator answers the question that comes before that one: if you're still working and haven't built that fund yet, how much do you need to save each month, starting now, to have it ready by the time you actually start converting?
You can, but it defeats much of the point. Every dollar used to pay the conversion tax is a dollar that doesn't get the Roth account's decades of tax-free growth — and if you're under 59½, money withdrawn from the Traditional side to cover the tax bill can also trigger the 10% early withdrawal penalty on top of the tax itself. Prefunding the bridge in a separate taxable account avoids both problems.
That depends on how close you are to needing each rung's cash. Money for a tax bill due in the next year or two is usually better held in something stable — a high-yield savings account, a money market fund, or short-term Treasuries — since a market drop right before you need to write the check can force you to sell at a loss. Money for tax bills further out has more room to sit in a normal taxable brokerage account and grow, which is exactly why this calculator includes the capital-gains gross-up toggle: if you're investing the fund rather than parking it in cash, the growth itself creates a smaller, secondary tax bill you also need to cover.
A common approach is a mini bond ladder inside the bridge fund itself — laddering maturities to roughly match when each rung's tax bill comes due, so you're not forced to sell anything early. That's a level of detail beyond what this calculator models, but it's the natural next step once you know your target number.
Five years is the standard assumption, since that's how long each rung takes to become accessible — but if you're already retired and living off other savings for part of that window, or want a bigger cushion, the prefund window above is adjustable up to 25 years.
No — this tool assumes your Traditional IRA balance is 100% pre-tax. If you have after-tax (non-deductible) contributions mixed in, the IRS requires you to convert a proportional blend, which changes the taxable portion of each conversion. Consult a CPA if that applies to you.
If you invest the prefund money in a taxable brokerage rather than holding cash, its growth will owe capital gains tax when you sell to pay the conversion bill. The gross-up toggle inflates your savings target so the after-tax amount you're left with still covers the full tax bill.
"Real" here means already adjusted for inflation, so you shouldn't enter a raw stock-market average like 10%. A widely used long-run estimate for a diversified stock/bond portfolio, after inflation, is somewhere in the 4–6% range — the calculator defaults to 5%. If the bridge fund is mostly cash or short-term bonds instead (see above), a more conservative 1–3% is more realistic. The number you pick matters more the longer your horizon is, so it's worth revisiting this assumption periodically rather than setting it once and forgetting it.
Re-run the numbers with an updated "years until conversions start." A shorter horizon means a higher required monthly contribution to hit the same target; a longer one gives your existing savings more time to compound, which can lower it — sometimes enough to show you're already on track. There's no penalty for checking in on this more than once; it's meant to be revisited as your timeline firms up.
The core bet behind any Roth conversion is that you're paying tax now at a rate you expect to be lower than what you'd otherwise pay later — whether that's because your income drops in early retirement, or because you think rates in general will rise. Future legislation could shift brackets in either direction, which is outside what any calculator can predict. This tool uses current-law brackets as a planning baseline; it's worth re-checking your assumptions if tax law changes materially before you start converting.