Last verified April 2026
Index Fund vs ETF Inside a 401(k), IRA, or HSA (2026)
The Most Important Sentence on This Page
Inside an IRA, 401(k), or HSA, the tax-efficiency difference between ETFs and index mutual funds is completely irrelevant. You don't get taxed on distributions in these accounts anyway. Pick based on availability, expense ratio, and convenience.
Roth IRA and Traditional IRA
Any IRA allows both ETFs and mutual funds. The relevant differences are broker availability and minimum investment. Which type of IRA to use (Roth vs Traditional) is a separate question - see traditionaliravsrothira.com for that analysis. Here we focus on which wrapper (ETF vs MF) to use inside your chosen IRA.
| Broker | ETFs available? | Mutual funds available? | Best options |
|---|---|---|---|
| Vanguard IRA | Yes | Yes | VTI or VTSAX (identical). Either is fine. VTI for portability; VTSAX for simplicity. |
| Fidelity IRA | Yes | Yes | FXAIX (0.015%) or VTI/VOO. FXAIX is cheapest; VTI/VOO for portability. |
| Schwab IRA | Yes | Yes | SWPPX (0.02%) or SCHB/VOO. Either is excellent. |
| Robinhood IRA | Yes (ETFs only) | No | VTI, VOO, VXUS, BND as core four. No Vanguard/Fidelity MFs. |
| M1 Finance IRA | Yes (pies) | Limited | Any ETF in M1 universe via pie allocation. Great for three-fund portfolio. |
401(k) - The Operational Reality
401(k) plans are administered by record-keepers (Fidelity, Empower, Vanguard, Principal, TIAA, Voya, T. Rowe Price, Alight, John Hancock). Their infrastructure was built around end-of-day NAV settlement: participant contributions, loan repayments, hardship withdrawals, and rebalancing trades are all processed in a nightly omnibus batch at that day's NAV.
ETF intraday execution - where the "price" is whatever the exchange says at the moment of trade - doesn't map cleanly into this omnibus-NAV model. The accounting becomes complicated: if 200 participants' trades are batched together, what intraday price gets applied to each? The ERISA fair-dealing requirement creates liability risk for plan sponsors who execute trades at varying intraday prices. This is why most 401(k) plans don't offer ETFs - it's an operational and liability issue, not a regulatory ban.
If your 401(k) offers a brokerage window
Some modern plans offer a self-directed brokerage window (Schwab PCRA, Fidelity BrokerageLink, Merrill PlanConnect). Through these, participants can buy ETFs and individual stocks outside the core menu. Verify the fees: brokerage windows typically carry a flat $50-$150 annual fee plus per-trade commissions. For most participants, the low-cost index mutual funds in the core menu are the better choice despite the ETF availability.
The right strategy for a 401(k) is simple: identify the lowest-expense-ratio broad-market index fund in your plan menu and invest in it. Common examples: FXAIX (Fidelity-administered plans), VINIX or VIIIX (Vanguard institutional S&P 500), FSMAX (Fidelity total market), VEMPX or VIIIX. If none are available, use the cheapest target-date index fund as a proxy. See 403bvs401k.com for public-sector plan specifics.
HSA (Health Savings Account)
HSAs with investment capability (Fidelity HSA, Lively HSA + Schwab brokerage, HealthEquity, Optum Bank) function essentially like brokerage accounts. Fidelity HSA is generally the best for investors: no account fees, full brokerage access to all ETFs and mutual funds. If you're using your HSA as a stealth retirement account (paying medical expenses out of pocket now, letting the HSA compound, reimbursing yourself decades later), invest the HSA in broad-market index ETFs or mutual funds exactly as you would an IRA - with tax efficiency being irrelevant inside the account.
Best ETFs for a Roth IRA (Core Portfolio)
| ETF | ER | Role in portfolio | Notes |
|---|---|---|---|
| VTI | 0.03% | US total market core | ~70-80% of equity for US-only; reduce to 50-60% for global |
| VXUS | 0.08% | International equity | 20-40% depending on your US/intl preference |
| BND | 0.03% | US total bond market | Match bond allocation to your risk tolerance |
| VNQ | 0.12% | Real estate (REIT) | Optional 5-10% for real estate exposure |
Alternative: a single Vanguard target-date fund (e.g. VFFVX for ~2055 retirement) handles the allocation automatically and glides toward more bonds as you approach retirement. It's a one-fund Roth IRA solution. The trade-off: slightly less control over your US/international ratio and a slightly higher combined ER (~0.08-0.10%) than a self-built three-fund portfolio. For which IRA type, see 401kvsrothira.com.