ETF Overlap Detector
Detect hidden overlap between ETFs by comparing their top holdings. Identify concentration risks in your portfolio.
How It Works
The ETF Overlap Detector compares the top holdings of two or more ETFs to measure how much they share in common. You enter the ETF names and paste in their top 10 holdings from the issuer's website. The tool then computes pairwise overlap percentages and an overall concentration score.
This helps you avoid accidentally over-concentrating in the same stocks across multiple ETFs. For example, if you own VOO, IVV, and SPY — all three track the S&P 500 and have near-100% overlap. The tool makes this overlap visible so you can make informed allocation decisions.
The Formula
For each pair (A, B):
S_A = set of tickers in ETF A
S_B = set of tickers in ETF B
overlapPct = (|S_A ∩ S_B| / min(|S_A|, |S_B|)) × 100
Concentration Score = average of all pairwise overlapPct values
Tickers are compared case-insensitively. Duplicate tickers within the same ETF are deduplicated.
FAQ
Why should I care about ETF overlap?
When you own multiple ETFs that hold the same stocks, you are not as diversified as you think. The ETF Overlap Detector shows you exactly which stocks appear in multiple ETFs so you can see your real concentration risk.
How is overlap percentage calculated?
The calculator compares each pair of ETFs by looking at their top holdings. It counts how many tickers appear in both ETFs and divides by the size of the smaller holdings list. A 100% overlap means one ETF's holdings are a complete subset of the other.
What does the concentration score mean?
The concentration score is the arithmetic average of all pairwise overlap percentages. If you have 3 ETFs, the score is the average of 3 pairwise comparisons.
What is a good overlap score?
Below 40% is low overlap — your ETFs are well diversified. 40-70% is moderate — some concentration exists. Above 70% is high — you are paying multiple expense ratios for very similar exposure.
Where can I find my ETF's top holdings?
You can find an ETF's top holdings on its issuer website, Morningstar, ETF.com, or Yahoo Finance. Copy-paste the ticker symbols, separated by commas.
Related Tools
Pair this with the Portfolio Rebalancer to adjust your allocation after identifying overlap. Use the Stock Chart to visualize individual holdings.