401(k) vs Roth IRA: Stock Investing Tax Wrappers Compared
Compare 401(k) and Roth IRA accounts for stock investing — tax treatment, contribution limits, employer match, withdrawal rules and which to fund first.
401(k) Basics
A 401(k) is an employer-sponsored retirement plan. Contributions are deducted from your salary, often with an employer matching contribution. There are two flavours:
- Traditional 401(k): contributions are pre-tax. They reduce your taxable income now, grow tax-deferred, and are taxed as ordinary income when withdrawn in retirement.
- Roth 401(k): contributions are post-tax. No deduction now, but qualified withdrawals in retirement (after age 59½ and 5 years) are entirely tax-free.
For 2025, the employee contribution limit is $23,500 (the IRS lifted it from $23,000 in 2024). Workers aged 50+ can contribute an additional $7,500 catch-up; ages 60–63 can contribute $11,250 under SECURE 2.0.
Roth IRA Basics
A Roth IRA (Individual Retirement Account) is a post-tax retirement account you open yourself, not through an employer. You contribute money on which you have already paid tax, and qualified withdrawals — including all the growth — are 100% tax-free.
For 2025, the contribution limit is $7,000 ($8,000 with the age-50+ catch-up). Contributions are subject to income limits — the phase-out for single filers starts at $150,000 and ends at $165,000 of modified adjusted gross income; for married filing jointly, $236,000 to $246,000.
Side-by-Side Comparison
| Feature | Traditional 401(k) | Roth IRA |
|---|---|---|
| 2025 contribution limit | $23,500 (+$7,500 50+) | $7,000 (+$1,000 50+) |
| Tax treatment of contributions | Pre-tax (deduction now) | Post-tax (no deduction) |
| Tax treatment of withdrawals | Taxed as ordinary income | Tax-free if qualified |
| Employer match | Common (3–6% of salary) | None |
| Income limits to contribute | None | Phases out from $150k single / $236k MFJ |
| Investment choices | Limited menu set by plan | Almost any stock, ETF, or fund |
| Required Minimum Distributions | From age 73 | None during owner's lifetime |
| Early-withdrawal penalty | 10% before 59½ (with exceptions) | Contributions anytime; growth 10% before 59½ |
Tax: Now vs Later
The deepest difference is timing of taxation:
- Traditional 401(k) defers tax. Better if you expect a lower marginal tax rate in retirement than now.
- Roth IRA pays tax now. Better if you expect an equal or higher tax rate in retirement, or if you simply value the certainty of tax-free withdrawals.
For high earners in their peak years, traditional usually wins. For younger workers in early-career tax brackets, Roth usually wins. Many people benefit from holding both — a practice known as "tax diversification" — so they have control over taxable income in retirement.
Employer Match — Free Money
Almost every retirement-planning rule starts with the same line: contribute enough to your 401(k) to capture the full employer match. A typical match is 50% of contributions up to 6% of salary — which, on a $80,000 salary, is up to $2,400 a year of free compensation. The match is an instant 50%–100% return on contributions, before any market growth, and there is no equivalent in any other account type.
Note: many employer matches still vest over 3–6 years. Check your plan documents.
Investment Choices
Inside a 401(k) you are stuck with whatever fund menu your employer has chosen. The average plan has 15–25 options, often dominated by target-date funds and a few index funds. Costs vary widely — some plans offer 0.05% Vanguard funds, others charge 1.0%+ for similar exposure. Always look at the expense ratio of every option before choosing.
A Roth IRA you open yourself at Fidelity, Schwab, Vanguard or any major broker has access to virtually any US-listed stock, ETF, or mutual fund. For most people, that means the Roth IRA can hold the cheapest possible global index ETF.
Income Limits for the Roth IRA
2025 Roth IRA contribution phase-outs:
| Filing Status | Full Contribution | Phase-out Range | No Contribution |
|---|---|---|---|
| Single / HoH | Below $150,000 | $150,000–$165,000 | Above $165,000 |
| Married filing jointly | Below $236,000 | $236,000–$246,000 | Above $246,000 |
Which to Fund First
The widely-used "funding waterfall" for most US workers:
- 1. 401(k) up to the full employer match. Free money first.
- 2. HSA if you are eligible — uniquely triple tax-advantaged.
- 3. Roth IRA up to the limit. Wide investment choice, tax-free growth, no RMDs.
- 4. 401(k) up to the federal limit. Big-tax-bracket wealth-builder.
- 5. Mega Backdoor Roth or taxable brokerage if you have more to save.
Adjust if your employer match is unusually generous (you might want to keep going to the federal limit before the Roth IRA), or if you do not have access to a 401(k) at all.
Backdoor Roth IRA (Briefly)
Earners above the Roth IRA income limit can still contribute via the "backdoor": make a non-deductible contribution to a traditional IRA, then convert it to a Roth IRA shortly after. The conversion itself is tax-free as long as you have no other pre-tax IRA balances (the IRS pro-rata rule). Mega-backdoor refers to a similar process inside some 401(k) plans, allowing post-tax contributions up to ~$70,000/year in 2025 — only available if your plan supports it.
Worked Example: $500/Month for 30 Years
Investing $500/month for 30 years at 7% real return:
| Account | Account Value | Tax Treatment | Spendable in Retirement |
|---|---|---|---|
| Roth IRA | $612,000 | Tax-free withdrawal | $612,000 |
| Traditional 401(k) at 22% retirement bracket | $612,000 | Taxed as income | ~$477,000 |
| Traditional 401(k) at 12% retirement bracket | $612,000 | Taxed as income | ~$539,000 |
| Taxable brokerage (long-term gains @ 15%) | $612,000 gross — but lower after annual taxes drag | Capital gains tax + dividend tax along the way | ~$430,000–$480,000 |
The traditional 401(k) treatment depends entirely on the relative tax rates at contribution and withdrawal — but in any reasonable scenario the tax-advantaged accounts thrash an unwrapped taxable brokerage.
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