IRA, 401(k) & Roth vs. Taxable Brokerage: Which Account to Use
The choice between tax-advantaged and taxable accounts doesn’t determine what you buy — it determines how much of your gains you actually keep. Over 20-30 years, the tax treatment alone can represent tens of thousands of dollars on the same investment.
The three account types, side by side
Roth IRA / Roth 401(k)
Tax treatment: Contribute after-tax dollars. All growth and withdrawals in retirement are tax-free.
Limits (2025): $7,000/yr IRA ($8,000 if 50+). 401(k): $23,500 ($31,000 if 50+). Income limits apply for Roth IRA.
Constraint: Penalties for withdrawing earnings before 59½ (with exceptions). Roth IRA contributions (not earnings) can be withdrawn anytime.
Traditional IRA / 401(k)
Tax treatment: Contribute pre-tax dollars (tax deduction now). Growth is tax-deferred. Withdrawals in retirement taxed as ordinary income.
Limits: Same as Roth. Employer 401(k) match doesn’t count toward employee limit.
Constraint: Required Minimum Distributions (RMDs) starting at 73. Early withdrawal penalties apply.
Taxable brokerage
Tax treatment: No tax advantage. Dividends and realized gains taxed annually. Long-term capital gains: 0/15/20% depending on income.
Limits: None. No contribution cap, no income restrictions.
Constraint: None. Full flexibility — withdraw anytime, invest in anything, no penalties.
The real impact of taxes: a worked example
Consider $300/month invested for 25 years at a hypothetical 7% annual return. The portfolio reaches approximately $243,000, with $153,000 in gains.
| Account | Tax on $153,000 gains | Net after tax |
|---|---|---|
| Roth IRA | $0 | ~$243,000 |
| Traditional IRA (22% bracket) | ~$53,500 (on full withdrawal) | ~$189,500 |
| Taxable (15% LTCG) | ~$23,000 (on gains only) | ~$220,000 |
The Roth advantage over taxable: $23,000 — roughly 6 years of monthly contributions saved by tax treatment alone. And the Traditional IRA, despite the upfront deduction, produces the lowest net amount if the investor is in a similar tax bracket at withdrawal.
The decision logic
Step 1: Capture the employer match. If your employer offers a 401(k) match, contribute at least enough to get the full match. It’s an immediate 50-100% return on your money — no investment can replicate that.
Step 2: Max out Roth space if eligible. For most young or moderate-income investors, the Roth IRA is the most powerful vehicle — tax-free growth for decades. Income limits apply ($161,000 MAGI for single filers in 2025), but the backdoor Roth conversion remains available for higher earners.
Step 3: Fill remaining tax-advantaged space. After the Roth, use remaining 401(k) space (Traditional or Roth, depending on current vs. expected future tax bracket). If available, an HSA (Health Savings Account) offers a triple tax advantage and functions as a stealth retirement account.
Step 4: Taxable brokerage for everything else. Once tax-advantaged space is exhausted, the taxable account offers unlimited capacity and full flexibility. Tax-loss harvesting, qualified dividends (taxed at LTCG rates), and the step-up in cost basis at death provide meaningful tax optimization even without sheltered status.
What most comparisons forget
Tax law changes. Contribution limits, income thresholds, LTCG rates, Roth conversion rules — all of these can change legislatively. An investor making 30-year decisions based on current tax law is making an implicit bet that the rules won’t change. Optimize, but don’t over-optimize to the point of fragility.
The account doesn’t replace the strategy. A Roth IRA filled with speculative meme stocks will underperform a taxable account holding a total market ETF for 20 years. The account optimizes what you keep — it doesn’t determine what you earn. Performance comes from the method, not the vehicle.
Taxes are a nominal cost. Like fees and inflation, taxes erode real returns. The real vs. nominal returns page shows how these three layers of erosion — fees, inflation, taxes — transform a gross 7% return into a much lower net real figure.
Going deeper
The sub-pillar Anatomy of Investments deconstructs the real returns of each asset class after all layers of erosion: fees, inflation, taxes, and investor behavior. That’s where the gap between a displayed return and an effective return becomes visible.
Next step
Account chosen, method in place. The next question is natural: how much should you invest each month? The answer is less obvious than it seems — because the parameter that determines the final result isn’t the one you’d expect.
How much to invest per month →