How to Use ETF Comparison Tools
Comparing two ETFs on expense ratio alone misses the point. The number that surprises most investors is holdings overlap: two 'different' funds that own 80% of the same stocks.
Don't have time? Here's what you need to know:
- 1The most valuable thing a comparison reveals is holdings overlap; two 'different' funds can own 80%+ of the same stocks.
- 2When two funds track the same index, the decision collapses to expense ratio and broker availability.
- 3Compare total return (with dividends) over identical periods, and always read return alongside volatility.
- 4Real diversification comes from assets that behave differently, not from stacking funds that hold the same names.
What a Comparison Tool Lets You See
An ETF comparison tool lines up two or more funds across the metrics that decide which to own: expense ratio, the index each tracks, top holdings, sector weights, fund size, and historical return. The value isn't any single number; it's seeing them together, because the right choice depends on how the metrics trade off. A slightly higher fee can be worth it for materially different exposure, and a lower fee is meaningless if the two funds own essentially the same thing.
The most useful comparisons are between genuine alternatives you're choosing among, two S&P 500 funds, two dividend funds, a growth fund versus a value fund, not random pairings. When the funds track the same index, the comparison collapses to cost and structure. When they track different indexes, the comparison is really about which exposure you want, and the fee is secondary.
The Holdings-Overlap Trap
The single most valuable thing a comparison reveals is holdings overlap, the percentage of two funds' portfolios that consists of the same securities. Investors routinely buy several funds believing they're diversifying, only to discover the funds own largely the same large-cap U.S. stocks. An S&P 500 fund and a total U.S. market fund like VOO and VTI overlap heavily, because the S&P 500's giants dominate both. Owning both adds complexity without much real diversification.
The same trap appears with a tech-sector fund and a broad market fund, since the biggest companies in the index are already technology giants. Genuine diversification comes from combining assets that behave differently, U.S. and international stocks, stocks and bonds, not from stacking funds that hold the same names. A comparison tool that shows overlap saves you from accidentally concentrating when you meant to spread out.
Important: Two funds with 80%+ holdings overlap aren't diversification, they're one bet held twice. Check overlap before assuming a second fund adds anything.
Reading the Numbers Without Being Fooled
When you compare returns, make sure you're looking at total return, which includes reinvested dividends, not just price change, because a fund with a lower price gain but higher dividends can deliver more overall. Also compare over identical periods; a fund launched in 2015 will look better or worse than a 1995 fund simply because of which years each lived through. And never read a single headline return without the volatility beside it, two funds with the same average return but very different swings are not equally good.
The table below shows the kind of side-by-side a good comparison produces, here for two S&P 500 funds that track the identical index. Notice how little separates them: when the index is the same, the decision is essentially the expense ratio and which fund your broker offers commission-free.
| Metric | VOO | IVV |
|---|---|---|
| Index | S&P 500 | S&P 500 |
| Expense ratio | 0.03% | 0.03% |
| Holdings overlap | ~100% | ~100% |
| Structure | Open-end fund | Open-end fund |
| Decision factor | Broker availability, preference | Broker availability, preference |
Tip: Always compare total return over the same time window, and read return and volatility together; an average return without its risk tells you almost nothing.
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Putting a Comparison to Work
Use a comparison at two moments. First, when you're choosing between final candidates a screener produced, the tool settles the tie on fee, structure, and overlap. Second, when you already own several funds and want to check you're not unknowingly doubling up, comparing your holdings exposes hidden overlap before it quietly concentrates your portfolio.
The Compare Any tool handles the head-to-head on fee, holdings, and key stats, while the Portfolio X-Ray goes further by analyzing your entire set of holdings at once to surface overlap and true asset-class exposure across every account. Together they answer the two questions that matter: which of these funds should I buy, and do the funds I already own actually diversify me?
Frequently Asked Questions
What should I compare when choosing between two ETFs?
Compare the index each tracks, the expense ratio, top holdings and sector weights, holdings overlap, fund size, and total return over identical periods. When two funds track the same index, the decision narrows to cost and structure. When they track different indexes, the comparison is really about which exposure you want, and the fee becomes secondary.
What is holdings overlap and why does it matter?
Holdings overlap is the percentage of two funds' portfolios made up of the same securities. It matters because investors often buy multiple funds thinking they're diversifying, when the funds actually own largely the same large-cap stocks. High overlap means you're holding one bet twice rather than spreading risk, so checking it prevents accidental concentration.
Why do an S&P 500 fund and a total-market fund overlap so much?
Because the S&P 500's largest companies dominate both. A total U.S. market fund holds thousands of stocks, but it's weighted by size, so the same mega-cap names that make up the S&P 500 also make up most of its value. The result is heavy overlap, which is why owning both adds complexity without meaningfully more diversification.
Further Reading
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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.