Key Takeaways
- A Roth IRA grows tax-free forever; a taxable account pays taxes on dividends, gains, and interest along the way.
- Taxable accounts win on liquidity and tax-loss harvesting; Roth wins on long-term compounding.
- For most long-horizon investors, the Roth's tax-free growth beats the taxable account's flexibility.
How a Taxable Account Taxes You
Money outside retirement accounts faces a rolling tax burden. Dividends are taxed each year — qualified dividends at 0/15/20% (plus the 3.8% Net Investment Income Tax above $200,000 single / $250,000 married), non-qualified at ordinary rates. Interest is always ordinary income. Capital gains are deferred until you sell, then taxed at 0/15/20% (short-term gains at ordinary rates). Even a tax-efficient index fund leaks roughly 0.5-1% of its return to taxes each year for a middle-income investor — a drag that compounds over decades. The Roth IRA eliminates all of it: no dividend tax, no capital gains tax, no tax on withdrawals, ever.
When the Taxable Account Wins
- Liquidity: no age restrictions, no five-year rules, no 10% penalties — money is available anytime.
- Tax-loss harvesting: selling losers to offset gains and up to $3,000 of ordinary income each year — unavailable inside an IRA.
- Basis step-up at death: heirs receive a stepped-up cost basis, wiping out built-in gains entirely — arguably better than inheriting a Roth in some estate plans.
- The 0% capital gains bracket: taxpayers in the 12% ordinary bracket pay 0% on long-term gains — a genuinely tax-free outcome with no contribution limits.
The Long-Run Comparison
Run a 25-year horizon at 7% gross with a 0.8% annual tax drag on the taxable account: $50,000 grows to about $233,000 in the taxable account versus $271,000 in the Roth — a $38,000 gap, and the Roth's advantage widens with every additional contribution year. The conversion question is different: converting $50,000 at 24% costs $12,000 today, which must be earned back by the tax savings — typically 5-10 years depending on your rates. If your horizon is shorter, or you need the flexibility, the taxable account wins; if you are investing for 15+ years, the Roth conversion usually wins on math alone.
Action Steps
- Estimate your annual tax drag on the taxable account (dividends + realized gains × your rates).
- Compare against the conversion tax using the home-page calculator.
- If you convert, keep the taxable account for short-term needs and emergency funds.
- Use tax-loss harvesting in the taxable account regardless — it helps either way.
Worked Example: The 25-Year Comparison
Run the two paths side by side. Sarah, 40, has $50,000 she can either convert to a Roth (paying 24% tax from cash) or leave in a taxable brokerage account. Roth path: $50,000 grows at 7% for 25 years to about $271,000 — every dollar tax-free. Taxable path: the same $50,000 grows at a 6.2% after-tax rate (7% less a 0.8% annual drag from dividends and turnover) to about $218,000, and withdrawing it triggers capital gains tax on the gains — maybe $15,000-$20,000 more in tax, leaving roughly $200,000. The Roth wins by about $70,000. Now add the conversion tax: Sarah paid $12,000 from cash, so the Roth's net advantage is still roughly $58,000. The taxable account only wins if Sarah needs the money before 59½, wants to tax-loss harvest, or expects to die with the account (heirs get a step-up in basis). For pure long-term wealth, the Roth conversion is the better machine.
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Use the Calculator →The Long-Term Comparison
Compare a $50,000 conversion versus a $50,000 taxable investment, both growing 7% for 25 years. The Roth grows to about $271,000 with zero tax at withdrawal. The taxable account also grows to roughly $271,000 pre-tax, but you owe capital gains tax on the growth — at 15% that is about $33,000, leaving $238,000, and dividends were taxed along the way, shaving further. The Roth wins by roughly $40,000-50,000 in this scenario — before considering that the conversion itself cost tax today. The conversion only wins if today's tax rate is lower than the effective tax rate on the taxable account's future gains plus the tax drag of dividends. For high earners in the 32%+ bracket with decades to go, the taxable account sometimes wins because the conversion tax is so large. The deciding factor is always the rate comparison — run the numbers at your actual brackets rather than assuming Roth is automatically better.