ETFs and index funds in your 401(k)
The fund-selection question lives downstream of the wrapper-choice question. Once you've decided to fund the 401(k), you pick from a limited menu the plan offers (typically mutual funds, not ETFs). Here is how to read the menu, why ETF-vs-mutual-fund matters less in a tax-deferred wrapper, and how the ERISA fiduciary regime constrains what your plan can charge you.
Wrapper choice matters more than ETF-vs-mutual-fund choice
Inside a 401(k) or IRA, the tax-deferred wrapper neutralises the main ETF advantage (no capital-gains distributions). What still matters: expense ratio, diversification, glide path.
ETF tax-cost advantage is real
The ETF in-kind redemption mechanism avoids capital-gains distributions, saving 0.20-0.80% per year for an investor in the 20-37% bracket under 26 U.S.C. § 1(h) long-term capital gains rates. See ETFvsIndexFund.com for the deep dive.
Tax-deferred wrapper neutralises it
No annual tax bill on distributions regardless of vehicle. The ETF tax-cost advantage is effectively zero. Expense ratio dominates: a 0.04% S&P 500 index mutual fund (VFIAX) and a 0.03% S&P 500 ETF (VOO) are functionally identical inside a 401(k).
What your fee disclosure must tell you
The DOL participant-fee-disclosure regulation gives you the right to see every fee charged to your account. Use it.
Annual disclosure must include
- Plan-level fees: recordkeeping, administrative, legal, accounting (typically $20-80 per participant per year).
- Investment-specific fees: expense ratio, 12b-1 fees, transaction costs, redemption fees.
- Comparative chart of designated investment alternatives: all options on the menu side-by-side with 1, 5, and 10-year returns and total expense ratios.
- Quarterly statements: actual dollar fees charged to your account that quarter.
- Service-provider compensation: per 29 CFR 2550.408b-2, all third parties paid more than $1,000 must be disclosed including indirect compensation (revenue sharing from fund families).
If your annual disclosure is missing or incomplete, that is a regulatory red flag. Report to DOL EBSA at askebsa.dol.gov.
What to do with the menu you have
Each portfolio satisfies the ERISA section 404(c) participant-direction safe-harbor diversification requirement (29 CFR 2550.404c-1) and the QDIA safe harbor (29 CFR 2550.404c-5) where applicable.
100% target-date fund
Pick the target-date fund nearest to age 65 (e.g., 2055 if you're 35 in 2025). Glide path auto-adjusts equity allocation as you age. Satisfies the QDIA safe harbor at 29 CFR 2550.404c-5. Typical expense ratio: 0.05-0.15% all-in at large employers, 0.30-0.60% at smaller employers.
60% US total / 30% intl / 10% bonds
If the plan offers a Vanguard, Fidelity, or Schwab US total-market index (~0.03-0.05% ER), an international index (~0.05-0.15% ER), and a total bond index (~0.03-0.05% ER), build the classic three-fund portfolio. Rebalance annually. Slightly cheaper than target-date funds, manual rebalancing required.
80% US / 20% intl, equity-heavy
Younger participants (under 40) with high risk tolerance may run 100% equities. Add bonds as you approach retirement. The plan menu must include at least three diversified options with materially different risk/return profiles to satisfy 29 CFR 2550.404c-1.
ETFvsIndexFund.com covers the taxable side
If you've maxed your 401(k) and Roth IRA and are investing in a taxable brokerage, the ETF-vs-mutual-fund decision becomes real. ETFvsIndexFund.com is the companion site for that decision.
Tax-cost ratio comparisons for VOO vs VFIAX, VTI vs VTSAX, and 30+ other ETF / mutual-fund pairs. When the wrapper changes (401k IRA Roth IRA taxable brokerage), the right vehicle changes too.
For your Roth IRA or Traditional IRA at a brokerage you control (Vanguard, Fidelity, Schwab), the full ETF universe is available. Pick by expense ratio and diversification, not by tax-cost (the IRA wrapper neutralises tax-cost differences).
Fund-selection questions
Why does my 401(k) menu only offer mutual funds, not ETFs?+
Historical operational reasons: 401(k) recordkeepers were built for daily-valued mutual funds, which trade once at the close (NAV). ETFs trade intraday at variable prices and were harder to support in plan accounting. The QDIA safe harbor at 29 CFR 2550.404c-5 also recognises target-date funds, balanced funds, and managed accounts (which are typically mutual-fund-based) as defaults. Some modern 401(k) recordkeepers now offer ETFs, but mutual funds remain the norm.
Does the ETF tax-cost advantage matter inside a 401(k)?+
Largely no. ETFs avoid capital-gains distributions through the in-kind redemption mechanism, which matters in a TAXABLE brokerage account. Inside a 401(k) or IRA the tax-deferred wrapper makes the distinction nearly irrelevant for return purposes (no annual tax bill on distributions regardless of wrapper). Expense ratio still matters in both wrappers. See ETFvsIndexFund.com for the full taxable-vs-tax-deferred breakdown.
What expense ratios should I expect in a 401(k)?+
Target-date funds in mid-to-large 401(k) plans typically run 0.05% to 0.50% all-in. S&P 500 index funds run 0.02% to 0.20%. Total-market index funds run 0.03% to 0.25%. International index funds 0.05% to 0.40%. Above 1% all-in (typically actively managed or annuity-wrapped) is high enough that it materially erodes long-term returns; you have the right under 29 CFR 2550.404a-5 to see the exact fee schedule on your annual disclosure.
Should I pick the target-date fund or build my own portfolio?+
Target-date funds are designed to satisfy the QDIA safe harbor at 29 CFR 2550.404c-5: diversified, professionally managed, age-appropriate glide path. For most participants this is the right default. Building your own portfolio (split across an S&P 500 index, an international index, and a bond index) can be slightly cheaper but requires manual rebalancing. Either approach satisfies the participant-direction safe harbor at 29 CFR 2550.404c-1 if the plan offers at least three diversified options with materially different risk/return profiles.
What if my 401(k) menu only has high-fee options?+
Three remedies: (1) Capture the match (always); the match dominates fee drag in the short-to-medium term. (2) Petition HR to add lower-cost index funds; cite 29 CFR 2550.404a-5 (fee disclosure) and ERISA section 404(a)(1) (prudent-expert standard). (3) Once you exceed the match contribution level, redirect additional savings to a Roth IRA (under your control, any custodian, full ETF/index fund universe). Order: match in 401(k), then Roth IRA, then back to 401(k). See /strategy.