The question sounds simple. The answer isn't. Which is better — a Roth IRA or a traditional IRA? The internet has an answer ready: Roth is better. Pay taxes now, never pay them again. Tax-free growth. Pass it on to your kids. The problem is that this answer ignores the most important variable in the entire equation: the tax rate you're paying now versus the tax rate you'd pay later. Roth is better when your current rate is lower than your future rate. Traditional is better when your current rate is higher. And for many retirees, the relationship between those two numbers is more complicated th
Three factors determine whether a Roth conversion or traditional tax deferral is mathematically superior for a given person in a given year. Getting all three wrong leads to paying more tax than necessary over your lifetime.
This is the core of the analysis. A Roth IRA makes sense when you pay taxes at a lower rate today than you would on future distributions from a traditional IRA. A traditional IRA makes sense when the reverse is true. During working years, income is typically highest and so is the marginal rate. If a surgeon earning $500,000 converts $200,000 to Roth, they're paying 3537% federal tax on money that might — in retirement — only be taxed at 22% or 24%. That's not arbitrage. That's a loss. The conversion case gets stronger as income drops in early retirement. A retiree who goes from a $300,000 working-year income to $60,000 in early retirement drops several brackets — and converting during those low-income years locks in a rate that may be 1015 percentage points lower than what a future RMD at a larger account balance would require.
Required Minimum Distributions change the calculus significantly — often in ways that favor Roth conversions even when current and future tax rates appear comparable. A traditional IRA that grows to $1,500,000 by age 73 generates a first-year RMD of roughly $56,600. By age 80, if the account has continued growing, the annual RMD exceeds $74,000. Layered on top of Social Security and other income, those distributions can push a retiree into brackets far above what they would have paid in early retirement. Roth IRAs have no RMD requirements during the owner's lifetime. That means Roth balances can grow tax-free indefinitely, without forcing taxable income events onto the owner's return. This is the structural advantage the conventional wisdom gestures at, but rarely quantifies. Scenario Account Balance Annual RMD Estimated Tax at 73 at 24% Conservative: $500,000 ~$18,868 ~$4,528 $500K traditional IRA Mid-range: $1M $1,000,000 ~$37,736 ~$9,057 traditional IRA High: $2M $2,000,000 ~$75,472 ~$18,113 traditional IRA Roth IRA (any N/A $0 — no RMDs $0 balance) RMD amounts use IRS Uniform Lifetime Table distribution period factor of 26.5 at age 73 (Publication 590-B). Tax estimates are illustrative at 24% marginal rate.
When an estate plan includes leaving retirement assets to heirs, the tax rate of the heir — not just the owner — becomes part of the Roth vs. traditional calculation. Non-spouse beneficiaries who inherit a traditional IRA must distribute the entire account within 10 years under the SECURE Act rules. If those heirs are in their peak earning years, those distributions are layered on top of their existing income at potentially high marginal rates. Non-spouse beneficiaries who inherit a Roth IRA face the same 10-year distribution rule, but the distributions are generally tax-free. A parent converting at 22% to spare a child paying 32% or 37% on the same dollars isn't doing estate planning — they're doing tax arbitrage across generations.
The conventional wisdom 'Roth is always better' ignores the|The Roth vs. traditional question has a third dimension that most