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:
- 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.
- 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.
- 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.
Related tools and guides
- Bracket Calculator — find your 2026 annual conversion ceiling
- IRMAA Calculator — Medicare surcharge impact by conversion amount
- The Roth Conversion Golden Window — timing and sequencing strategy
- Social Security + Roth Conversion — the effective rate multiplier
- The Pro-Rata Rule — when you have after-tax IRA basis
- The 5-Year Rule — what applies (and what doesn't) after age 59½
- Complete Roth Conversion Strategy Guide
- Match with a fee-only Roth conversion specialist
Frequently asked questions
How does a Roth conversion calculator work?
This calculator runs two parallel projections side by side. Scenario A converts a set amount annually from your traditional IRA to a Roth during the golden window (retirement to RMD age), paying tax now at your current bracket. Scenario B leaves everything in the traditional IRA and takes Required Minimum Distributions later at a higher projected rate. The model tracks year-by-year balances, cumulative taxes paid, and after-tax wealth to show the lifetime difference — typically $100,000–$600,000 for a retiree with $1M–$3M in a traditional IRA.
How much can I save with a Roth conversion?
The savings depend on the rate differential between now and RMD time. A retiree who converts $100,000/year at 22% for 8 years instead of paying 32% on large RMDs later typically saves $150,000–$400,000 in lifetime federal taxes. The calculator above shows the exact number for your balance, conversion rate, and horizon. The savings are larger than simple bracket math suggests because Roth funds grow tax-free for decades with no RMDs, and large RMDs also trigger IRMAA Medicare surcharges on top of ordinary income tax.
What tax rate should I use for my future RMDs?
Most retirees with $1M+ in a traditional IRA should enter 32–37% as their projected RMD-era rate, even if their stated bracket is lower. Three compounding reasons: (1) RMDs stack on top of Social Security, pushing up to 85% of SS into the taxable zone and creating an effective marginal rate 10–15 points above the stated bracket; (2) Medicare IRMAA surcharges add $1,000–$6,000/year per person for incomes over $109,000 single/$218,000 MFJ; (3) a $2M IRA growing at 6% reaches $3.2M by age 75 — the RMD on $3.2M alone is $130,000, before SS or other income. Use the bracket calculator to see the stacked rate precisely.
When is the best time to do a Roth conversion?
The optimal window is between retirement and the year RMDs begin — age 73 for those born 1951–1959, age 75 for those born 1960+ (SECURE 2.0 § 107). During this gap, earned income has stopped and Social Security often hasn't started, creating the lowest tax brackets most retirees will see since young adulthood. A 62-year-old who retires and delays Social Security to 70 can have up to an 8-year IRMAA-free window to convert at 12–22% federal rates before SS income compresses bracket room. See the golden window guide for timing by birth year.
Should I convert all at once or spread it over years?
Spreading conversions over multiple years is almost always better. Converting the entire IRA in one year would push income into the 32–37% bracket and likely trigger multiple IRMAA tiers simultaneously. Instead, filling to the top of the 22% or 24% bracket each year — or stopping just below an IRMAA threshold — lets each dollar convert at a lower effective rate. A $2M IRA converted over 8–10 years at 22% saves roughly 10–15 percentage points per dollar compared to a one-year lump sum. See the multi-year conversion plan guide for a worked example.
Does this calculator include IRMAA or Social Security?
This calculator uses a simplified two-rate model — your current bracket rate and your projected future rate — so IRMAA surcharges and Social Security taxation stacking are not explicitly modeled. This means the lifetime savings shown are likely understated. To see the IRMAA impact specifically, use the IRMAA-Aware Calculator. For a complete picture of all four tax layers (federal bracket + SS torpedo + IRMAA + state tax), use the Total Roth Conversion Tax Calculator.
Get a real multi-year conversion plan
The calculator gives you the lifetime savings estimate. A fee-only specialist builds the actual plan: exact annual amounts that fill brackets without IRMAA spillover, Social Security stacking analysis, state tax, pro-rata calculation, and beneficiary strategy. Then they give you a number to execute and adjust it each year as brackets inflate and your situation evolves. Free match, no obligation.
Sources
- IRS Publication 590-B (2025), Appendix B, Table III — Uniform Lifetime Table. RMD divisors used in this calculator (e.g., age 73 = 26.5, age 75 = 24.6, age 80 = 20.2, age 85 = 16.0, age 90 = 12.2). irs.gov/publications/p590b
- SECURE 2.0 Act of 2022 (Pub. L. 117-328), § 325 — Roth 401(k) and Roth TSP accounts exempt from lifetime RMDs starting 2024. § 107 — RMD age increased to 73 (born 1951–1959) and 75 (born 1960+). irs.gov
- IRC § 86 — Taxation of Social Security benefits. Up to 85% of benefits included in gross income when combined income exceeds $34,000 (single) / $44,000 (MFJ). Conversion income stacks on Social Security in computing combined income. law.cornell.edu
- IRS Rev. Proc. 2025-32 — 2026 federal income tax brackets (referenced in rate guidance). irs.gov/pub/irs-drop/rp-25-32.pdf
RMD divisors from IRS Pub 590-B Uniform Lifetime Table (updated 2022, effective 2022+; unchanged for 2026). Calculator uses marginal-rate tax estimation and does not model IRMAA surcharges, Social Security taxation stacking, state income tax, or pro-rata rule adjustments. Results are illustrative estimates for planning purposes only — not tax advice. Verified April 2026.