Roth Conversion Lifetime Tax Savings Calculator

How much do Roth conversions actually save over your lifetime? This calculator runs two parallel projections — convert during the golden window vs. leave in traditional IRA — year by year, using IRS Uniform Lifetime Table divisors for RMD modeling.¹ Enter your numbers to see the total lifetime tax difference.

How this calculator works

A simple "pay X% now vs Y% later" back-of-envelope misses three important effects. This model simulates the full arc year by year:

1. Conversion phase (your current age → RMD age). Each year, the annual conversion amount leaves the traditional IRA and enters the Roth. Tax is paid at your current rate — assumed from outside money (a taxable brokerage or savings account). The remaining traditional IRA balance and the growing Roth both compound at the same return rate.
2. RMD phase (RMD age → planning horizon). In both scenarios, the remaining traditional IRA generates Required Minimum Distributions each year, calculated using IRS Uniform Lifetime Table divisors¹ and taxed at your projected future rate. In the "no conversion" scenario, a much larger balance produces much larger RMDs — often pushing income into a higher bracket and triggering IRMAA Medicare surcharges.
3. Roth compounding. Once in the Roth, funds grow tax-free with no RMDs (Roth IRAs are exempt from lifetime RMDs; Roth 401(k) accounts are also exempt starting 2024 under SECURE 2.0 § 325²). This decades-long tax-free compounding is often the largest single driver of lifetime savings.

What this calculator doesn't model

• IRMAA surcharges. Conversions that cross Medicare income thresholds add $975–$5,820/yr per person in Part B and D costs. In the "no conversion" scenario, large RMDs routinely trigger IRMAA — a hidden cost that makes leaving money in the traditional IRA worse than the tax rate alone suggests. Use the IRMAA calculator to check.
• Social Security taxation stacking. Once Social Security begins, up to 85% becomes taxable income (IRC § 86). Conversion income stacks on SS, and large RMDs can push more SS into the taxable zone. This is why the projected RMD-era rate is often higher than the stated bracket — it's more like an effective 35–40% on marginal dollars.
• State income tax. Nine states have no income tax on retirement distributions. High-tax states (CA, NY, MN) add 5–13% on both conversion income and RMDs — amplifying both the cost of converting and the cost of not converting.
• Pro-rata rule. If you have after-tax (non-deductible) contributions tracked on Form 8606, each conversion is partially tax-free, lowering your effective conversion tax cost. See the pro-rata rule guide.
• Outside taxable account. This model tracks IRA and Roth balances only. The money you spend on conversion taxes (Scenario A) comes from outside and reduces your total liquid wealth relative to Scenario B during the conversion years — the "lifetime tax savings" number is the right metric for comparing the two scenarios on equal footing.
• Beneficiary planning. Roth IRAs inherited by a non-spouse beneficiary must be distributed within 10 years — but distributions are tax-free. Traditional IRA distributions inherited under the 10-year rule are taxable, often pushing heirs into peak earning brackets.