Roth Conversion Calculator: When Does It Make Sense?

Key Takeaways

• The break-even is simple: convert when your future tax rate will be higher than today's.
• Rates are only part of the story — RMDs, IRMAA, heirs, and state taxes all matter.
• Run the calculator with realistic rate assumptions, not hopeful ones.

What the Calculator Actually Shows

The calculator on the home page compares three numbers: the tax cost of converting today, the after-tax value of leaving the money in a Traditional IRA, and the tax-free value of a Roth. The engine is the break-even rule: if your marginal rate now equals your marginal rate in retirement, converting and not converting produce identical after-tax results; convert only if you expect a higher rate later. The inputs matter more than the output — a 24% current rate versus a 22% future rate says "don't convert," while 22% now versus 24% later says "convert." The honest problem is that nobody knows their future rate, which is why the output should be treated as a scenario, not a prediction.

What the Calculator Cannot See

• RMDs: a large Traditional IRA forces distributions at 73 (75 if born 1960+), which can push you into higher brackets and trigger IRMAA — converting reduces both.
• Heirs: inherited Roth money is tax-free for beneficiaries; inherited Traditional money is taxable over 10 years — a legacy motive tilts toward conversion.
• Tax diversification: holding both pre-tax and Roth money gives you the option to choose your withdrawal source each year — a flexibility the math cannot price.
• State taxes and IRMAA: both add real costs the simple calculator ignores.

Scenarios That Favor Conversion

• Low-income years (unemployment, sabbatical, early retirement before pensions start).
• Young investors with small balances and decades of tax-free growth ahead.
• Large pre-tax balances that will generate outsized RMDs.
• Expectations of higher future tax rates (historically, a reasonable bet).

Scenarios That Do Not

• Peak earning years with marginal rates of 32% or more.
• Short time horizons where the compounding benefit is thin.
• Cash-flow constraints that force paying the tax from the conversion itself.
• Medicare-adjacent retirees whose income would spike over IRMAA thresholds.

Action Steps

1. Enter your real numbers into the calculator — balance, current rate, expected future rate, horizon.
2. Run it at three future-rate scenarios (your rate, ±5 percentage points).
3. If conversion wins in the middle scenario, execute a partial conversion sized to your bracket.
4. Re-run annually; the answer changes as your income and balances change.

How to Read the Calculator's Recommendation

The calculator's "Recommendation" card compares your tax cost today against the projected after-tax value of the Traditional IRA at your assumed future rate. Treat the output as a sensitivity table, not a verdict. The disciplined way to use it: (1) run the calculation at your current marginal rate and your best guess of your future rate; (2) rerun it with the future rate five points higher and five points lower; (3) if conversion wins in the base case and the high case, convert; if it only wins in the high case, you are betting on rate increases — convert a smaller amount; if it loses even in the high case, do not convert. Remember the model cannot see RMD-driven bracket creep, IRMAA, state tax, or legacy goals — those are the inputs you add yourself. A calculator that says "convert" in a low-income year and "don't convert" in a peak year is working correctly; the answer is supposed to change.

Understanding the Calculator's Output

A Roth conversion calculator compares two scenarios: keep the money in a Traditional IRA (paying tax on withdrawals) versus convert now (paying tax today, withdrawing tax-free). The key inputs are your current marginal tax rate, expected retirement rate, years until retirement, expected return, and the source of the conversion tax payment. The break-even rule: if your tax rate in retirement equals your rate today, the conversion is roughly a wash (assuming you pay the tax from outside funds) — the benefit comes from converting at a lower rate today than you expect to pay later. The calculator also reveals the hidden cost of paying the tax from the IRA itself: a $100,000 conversion at 24% leaves only $76,000 in the Roth, and that $24,000 lost to tax also loses decades of compounding. Most planners recommend converting when today's rate is at least 5-10 percentage points below your expected retirement rate.