Not All ETFs Are Created Equal
The ETF market has grown enormously, with thousands of funds now available covering everything from broad global indices to niche sectors and complex strategies. While this gives investors incredible choice, it also means due diligence matters. Before committing money to any ETF, run it through these six key evaluation criteria.
1. Expense Ratio
The expense ratio is the annual fee you pay, expressed as a percentage of your investment. For a broad index ETF tracking the S&P 500, expense ratios can be as low as 0.03%. For actively managed or niche ETFs, they can exceed 0.75% or more.
Over time, even a small difference in fees compounds significantly. Always compare the expense ratio of an ETF to similar funds before investing.
2. Underlying Index or Strategy
Understand exactly what the ETF holds. Key questions to ask:
- What index does it track, and how is that index constructed?
- Is it market-cap weighted, equal-weighted, or factor-based?
- Does it hold stocks, bonds, commodities, or a mix?
- Are there concentration risks — is it heavily weighted in a few holdings?
Two ETFs that both claim to track "technology stocks" can have very different compositions depending on how their underlying index is built.
3. Assets Under Management (AUM)
AUM reflects how much money is invested in the fund. Larger funds generally offer several advantages:
- Better liquidity — easier to buy and sell without moving the price.
- Lower tracking error — more resources to accurately replicate the index.
- Lower closure risk — small ETFs with low AUM are sometimes shut down by the issuer.
As a general rule of thumb, look for ETFs with at least several hundred million dollars in AUM for core portfolio positions.
4. Bid-Ask Spread
Unlike mutual funds, ETFs trade on exchanges with a bid price (what buyers will pay) and an ask price (what sellers want). The difference — the spread — is a hidden trading cost. For highly liquid, large ETFs the spread is typically very tight (pennies). For thinly traded niche ETFs, it can be much wider and erode returns, especially if you trade frequently.
5. Tracking Difference vs. Tracking Error
These two terms are often confused but measure different things:
- Tracking difference — how much the ETF's annual return deviated from its benchmark index. A negative tracking difference (ETF outperformed) is actually favorable.
- Tracking error — the volatility of that deviation over time. A consistently small difference is better than a wildly inconsistent one.
You can find these metrics on the fund's fact sheet or on ETF research sites.
6. Tax Efficiency and Distribution History
If you're investing in a taxable account, an ETF's tax efficiency matters. Check whether the fund has a history of distributing capital gains — these are taxable events even if you didn't sell anything. Most plain-vanilla index ETFs are highly tax-efficient thanks to the in-kind creation/redemption process. Actively managed ETFs and some bond ETFs may be less so.
A Quick Evaluation Checklist
| Factor | What to Look For |
|---|---|
| Expense Ratio | As low as possible relative to peers |
| Index/Strategy | Clearly defined, well-understood methodology |
| AUM | Preferably $500M+ for core holdings |
| Bid-Ask Spread | Tight spread, especially for frequent trading |
| Tracking Difference | Small and consistent |
| Tax Efficiency | Low capital gains distributions |
Final Thought
A thorough ETF evaluation takes only a few minutes but can meaningfully improve your long-term outcomes. By focusing on costs, construction, liquidity, and tax efficiency, you can confidently build a portfolio of funds that genuinely serve your financial goals.