Quick answer
Your 401(k) plan almost certainly offers only mutual funds. The ETF vs index fund debate does not apply here. What matters is: (1) contribute enough to get the full employer match, (2) pick the index fund with the lowest expense ratio, and (3) choose broad market exposure over narrow sector funds.
How to Read Your 401(k) Fund Menu
Most 401(k) plans offer 10-25 fund options. Here is what to look for when evaluating your choices:
1. Find the expense ratio
This is the single most important number. It is listed in your plan documents as a percentage. Below 0.10% is good. Below 0.05% is excellent. Above 0.50% is a red flag.
2. Look for "index" in the name
Funds with "index" in the name passively track a benchmark and have lower fees. Funds without "index" are typically actively managed with higher fees and worse long-term performance on average.
3. Check the asset class
A simple approach: put 70-90% in a US stock index fund (S&P 500 or total market), 10-20% in an international stock index fund, and 0-10% in a bond index fund. Adjust based on your age and risk tolerance.
4. Avoid these red flags
Actively managed funds with 0.50%+ expense ratios. Company stock funds (concentrates your risk). Sector-specific funds (too narrow for a core holding). Funds with "A shares" or "load" in the name (sales charges).
The One Number That Matters: Expense Ratio
In your 401(k), you are likely contributing $500-$2,000 per month for 20-30 years. Over that time horizon, the expense ratio compounds dramatically.
$500/month for 30 years at 0.05% ER
$680,191
Low-cost index fund
$500/month for 30 years at 0.50% ER
$638,684
Actively managed fund
Difference: $41,507 lost to fees over 30 years.
(Assumes 8% annual return before fees)
Common 401(k) Fund Options
After You Leave: Roll to an IRA
When you leave an employer, you can (and usually should) roll your 401(k) balance to an IRA at the brokerage of your choice. A rollover IRA gives you access to every ETF and index fund on the market, not just the limited options in your employer plan.
The process: contact your new brokerage (Vanguard, Fidelity, or Schwab) and tell them you want to initiate a direct rollover from your former employer's 401(k). They will guide you through the paperwork. A direct rollover (trustee-to-trustee) has no tax implications.
Once the rollover is complete, you can invest in any fund you want. This is when the ETF vs index fund choice actually matters for this money. See our Roth IRA guide for specific fund recommendations by brokerage.
2026 Contribution Limits
Employer match does not count toward the employee limit. Always contribute enough to get the full match, that is a 50-100% instant return.
401(k) FAQ
Can I buy ETFs in my 401(k)?
In most 401(k) plans, no. Employer retirement plans overwhelmingly offer mutual funds, not ETFs. Some newer plans (especially those using self-directed brokerage windows) may allow ETF purchases, but this is uncommon. Check your plan documents or ask your HR department.
How do I pick the best fund in my 401(k)?
Look for index funds with the lowest expense ratios. Most plans offer an S&P 500 index fund or total market fund. Expense ratios below 0.10% are good; below 0.05% is excellent. Avoid high-fee target-date funds and actively managed funds unless they are genuinely low cost. The most important thing is contributing enough to get the full employer match.
What are the 2026 401(k) contribution limits?
For 2026, the 401(k) contribution limit is $23,500 for employees under 50. If you are 50-59 or 64+, the catch-up contribution is $7,500 (total $31,000). Ages 60-63 get a higher catch-up of $11,250 (total $34,750). Employer matching contributions do not count toward these limits.
Should I roll my 401(k) to an IRA when I leave a job?
Usually yes. Rolling a 401(k) to an IRA at Vanguard, Fidelity, or Schwab gives you access to low-cost index funds and ETFs that your employer plan may not offer. A rollover IRA gives you full control over your investment choices. Contact your new brokerage to initiate a direct rollover (trustee-to-trustee transfer) to avoid any tax complications.