Roth Conversion Calculator for Ultra-High-Net-Worth Families

Not tax or legal advice. 2026 federal tax brackets verified from IRS Rev. Proc. 2025-32. IRMAA figures per CMS 2026. Consult a qualified tax advisor before executing any conversion.

For a $30M+ family, the conventional Roth conversion calculus — "convert only when your current rate is lower than your future rate" — produces the wrong answer. At UHNW income levels, both your current rate and your heirs' rate are likely 37%. The conversion math is almost never about rate arbitrage. It's about (1) compounding inside a tax-free account versus a tax-deferred one, (2) removing future RMD income from your estate, and (3) paying today's income tax bill out of money that would otherwise sit in a taxable estate facing a 40% estate tax.

This calculator runs all three factors. Enter your situation and it shows the year-by-year Roth advantage, the break-even date, and whether the conversion crosses an IRMAA cliff.

How the calculator works

The comparison has two scenarios:

Convert: You convert $X from a Traditional IRA to a Roth IRA today, paying income tax from outside taxable funds. The Roth grows at your expected return, and your heirs inherit it income-tax-free (10-year rule with no annual RMD requirement — the Roth IRA owner has no required beginning date).

Don't convert: The Traditional IRA stays and grows at the same rate. The conversion tax you didn't pay stays in your taxable account and compounds at the after-tax rate (7% return × 76.2% = 5.3% after-tax, using the 23.8% combined LTCG+NIIT rate¹). Your heirs inherit the Traditional IRA, subject to annual RMDs if you die after your required beginning date,² and pay income tax at their marginal rate on all distributions.

The Roth advantage at any year = Roth value − (Traditional IRA after-heir-tax + forgone tax compounded at after-tax rate).

IRMAA: the most common conversion mistake

IRMAA (Income-Related Monthly Adjustment Amount) surcharges apply to Medicare Part B and Part D premiums when MAGI exceeds certain thresholds. In 2026, the surcharge structure for married filing jointly is:³

IRMAA uses income from two years prior (2024 MAGI determines 2026 premiums). Surcharges are per person — a couple both on Medicare faces double the per-person amount. The cliff structure means $1 over a threshold triggers the full higher surcharge; consider splitting a large conversion across two calendar years to straddle a cliff.

The estate tax angle most advisors miss

For families with taxable estates above the $15M per-person exemption (permanent under OBBBA, July 2025⁴), every dollar paid in conversion income tax is a dollar that leaves your taxable estate. The federal estate tax rate is 40%. So a $200,000 Roth conversion that costs $74,000 in income tax removes $74,000 from your estate — saving approximately $29,600 in estate tax. This benefit is immediate and certain, independent of growth rates or heir tax assumptions.

The implication: for large estates, the true after-tax cost of a Roth conversion is meaningfully lower than the income tax rate suggests. A 37% federal conversion tax on a $200K conversion costs $74K in income tax but only $44K in real economic cost once the estate tax savings are counted ($74K income tax paid − $29.6K estate tax avoided = $44.4K net cost, or a 22.2% effective economic rate on a $200K conversion).

Optimal conversion sizing at UHNW

Most UHNW families should not convert their entire traditional IRA in one year. Consider these sizing frameworks:

• Stay-within-bracket conversion. If any income falls in a bracket below 37%, convert up to (but not across) the 37% threshold: $768,700 of taxable income − other income − standard deduction = room for 35%-bracket conversion. Rare at true UHNW income levels, but relevant in retirement bridge years or sabbaticals.
• IRMAA-aware sizing. Size conversions to stay within the current IRMAA tier. A $50K conversion that keeps you in Tier 2 ($274K–$342K) is better than a $60K conversion that pushes you into Tier 3 — the IRMAA increase costs an additional $2,894/year per couple for as long as you're on Medicare.
• Estate + income tax stacking. For very large IRAs ($10M+) in a $100M+ estate, aggressive multi-year Roth conversion programs (converting $1–2M/year) can systematically move funds from a 40%-taxed estate into a tax-free asset class. The "tax cost" is largely offset by estate tax savings.
• Retirement bridge window. Between retirement and age 73 (when RMDs begin), UHNW families may have a temporary income gap if they've left employment. This is the ideal window to run larger conversions — income is lower, and the 2-year IRMAA lookback means careful timing can avoid IRMAA cliffs for the first two post-retirement years.

Inherited Roth vs. Traditional: the 10-year rule difference

Under T.D. 10001 (IRS final regulations, July 2024²): if you own a Traditional IRA and die after your required beginning date (April 1 of the year after reaching age 73), your beneficiaries must take annual RMDs in years 1–9 of the 10-year period, plus clear the account by year 10. These forced distributions often hit heirs in their highest-earning years at 37%.

Roth IRA owners have no required beginning date — Roth assets are never subject to lifetime RMDs. Inherited Roth IRAs always fall under the simple 10-year rule without annual interim distributions. The beneficiary can let the account compound tax-free for the full 10 years, then take all distributions income-tax-free. For a $3M inherited Roth at 7% growth, the 10-year tax-free compounding window adds approximately $2.9M in additional value compared to a Traditional IRA requiring annual taxable distributions.