Roth vs. Traditional IRA Tax Calculator
Last updated July 2, 2026
The Roth versus traditional IRA decision is fundamentally a tax rate arbitrage question: do you pay taxes now at your current marginal rate (Roth), or defer them until retirement at your future effective rate (traditional)? If your current marginal rate exceeds your expected future effective rate in retirement, traditional contributions produce better after-tax outcomes. If your future effective rate will be higher — because income will be substantial, because RMDs will push significant amounts into higher brackets, or because tax rates will have risen — Roth contributions are more valuable. For most people in the early-to-middle working years, the current marginal rate is at or near its career peak, making the traditional deduction most valuable. For younger workers in the 10 or 12 percent bracket, the Roth almost always wins.
The comparison is complicated by several factors the calculator should explicitly handle. Traditional IRA withdrawals in retirement increase Social Security taxability thresholds and are subject to Required Minimum Distributions starting at age 73, which can create forced income that pushes retirees into higher brackets than they'd choose. Roth accounts have no RMDs during the owner's lifetime and allow withdrawals that don't count against Medicare income thresholds or Social Security taxability calculations — tax advantages worth 3 to 8 percent of withdrawn amounts in some scenarios. Estate planning is another dimension: Roth accounts pass to heirs income-tax-free, while traditional accounts carry embedded tax liability. The optimal approach for many households is a mix — traditional contributions in high-earning years and Roth contributions or conversions in lower-income years or during the gap between retirement and RMD age.
Comparing your current marginal tax rate — the rate at which a traditional contribution saves taxes today — to your projected effective tax rate in retirement, including all income sources and the impact of RMDs. If the current rate is clearly higher, traditional wins. If the current rate is 12 percent or lower, Roth almost certainly wins. In the 22 to 24 percent range with uncertain future income, a combination approach or a Roth conversion strategy during lower-income years is often optimal.