
Roth IRA vs Traditional IRA: 5-Scenario Capital Gains Tax Decomposition
Upfront tax on Roth IRA contributions acts as a drag during prolonged market drawdowns, altering the break-even horizon. Traditional IRA deductions reinvested into taxable accounts can outperform Roth in bracket-compression scenarios. Asset location—placing VTI in Roth and BND in Traditional—adds approximately 40-60 bps of tax alpha annually. The 2020-2026 CAGR of US equities heavily skewed recent analyses toward Roth, hiding sequence-of-returns risks. The Core Mechanics of IRA Taxation Monthly $30K investment 20-year compound growth simulation The chart below shows a 20-year simulation of a $300 monthly investment (4%, 7%, and 10% annually). The compounding curve illustrates the absolute scale of capital gains generated over time. Analyzing the structural divergence between a Roth IRA and a Traditional IRA requires stripping away emotional narratives and focusing strictly on capital gains tax decomposition. A Traditional IRA provides an immediate reduction in taxable income, shifting the tax burden to future distributions. Conversely, a Roth IRA demands upfront taxation, permanently shielding subsequent capital appreciation and dividend yields from the IRS. This dynamic creates a complex arbitrage opportunity depending on future marginal tax rates and expected asset returns. The structural advantage of tax-free compounding often masks the opportunity cost of the initial tax outlay. [IRS.gov] ...

