Understanding ETF Benchmarks and Indices
Your ETF's benchmark is its North Star — the index it tries to match. Here is why the benchmark choice matters more than the fund itself.
Don't have time? Here's what you need to know:
- 1The benchmark determines your ETF's returns — asset class selection matters more than benchmark selection within an asset class
- 2A well-managed ETF should lag its benchmark by approximately the expense ratio — no more
- 3Compare ETFs against the same benchmark; cross-benchmark comparisons are meaningless
- 4Major benchmarks (S&P, CRSP, FTSE, MSCI) are all transparent, investable, and well-constructed
What a Benchmark Is and Why It Matters
An ETF's benchmark is the index it tracks. VOO's benchmark is the S&P 500. VTI's benchmark is the CRSP U.S. Total Market Index. The benchmark determines which stocks the ETF holds, how they are weighted, and what returns you should expect. Your ETF's returns will be approximately: benchmark return minus expense ratio.
Choosing the right benchmark (and therefore the right ETF) is more important than choosing the right fund within a benchmark. The difference between the S&P 500 and CRSP Total Market Index is about 0.1% per year. The difference between a U.S. stock benchmark and a bond benchmark is about 5% per year. Asset class selection trumps benchmark selection.
How to Evaluate Your ETF Against Its Benchmark
A well-managed ETF should underperform its benchmark by approximately its expense ratio — no more. VOO should return roughly S&P 500 minus 0.03%. If the gap is larger (say 0.20%), something is wrong: poor management, high cash drag, or excessive trading costs. Check the fund's annual report for actual vs benchmark returns.
Some ETFs slightly outperform their benchmark through securities lending income — Vanguard and iShares funds sometimes earn 0.01-0.03% annually from lending out the stocks they hold. This can partially or fully offset the expense ratio.
Tip: When comparing ETFs, always compare against the same benchmark. Comparing VOO (S&P 500 benchmark) to VXUS (FTSE International benchmark) is comparing apples to oranges. Compare VOO to IVV and SPY — all three track the S&P 500.
Frequently Asked Questions
Can an ETF change its benchmark?
Yes, though it is uncommon and must be disclosed to investors. Vanguard switched several ETFs from MSCI to FTSE benchmarks in 2012 to reduce licensing costs. The change was disclosed in advance and had minimal impact on holdings.
What makes a good benchmark?
A good benchmark is: transparent (published methodology), investable (you can actually buy all the stocks in it), representative (covers the intended market), and rules-based (not dependent on subjective decisions). Major benchmarks from S&P, CRSP, FTSE, and MSCI meet all criteria.
Should I care which index my ETF tracks?
For core holdings, the differences between major indices are minor. VOO (S&P 500) and VTI (CRSP Total Market) are both excellent. For international ETFs, the FTSE vs MSCI South Korea classification difference is worth knowing but not worth stressing over.
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Alex Harrington
CFA Level II Candidate, Finance & Economics
Alex Harrington is an independent ETF researcher and personal finance writer with over 8 years of experience analyzing exchange-traded funds. A CFA Level II candidate with a background in economics, Alex has reviewed 800+ ETFs and helped thousands of beginners build their first investment portfolios through clear, jargon-free education.
This content is for educational purposes only and does not constitute financial advice. Past performance does not guarantee future results. Consult a licensed financial advisor before making investment decisions.