Methodology
How every number on this site is produced, explained in plain English, with the fine print where it matters.
How overlap is calculated
Take every stock that both funds own. For each one, count the smaller of its two portfolio weights: if one fund has 7% in Apple and the other has 5%, they truly share 5%. Add those numbers up across all shared stocks, and the total is the overlap percentage.
5.0 + 6.5 + 2.4 = 13.9% overlap
In formula terms: overlap = Σ min(wA, wB) over every shared holding, the same convention institutional fund-comparison tools use.
How stocks are matched between funds
Two fund companies rarely describe the same stock the same way, so we match holdings by CUSIP, the standard ID number every US security has (with ISIN and ticker as backups). The same stock always matches no matter how each fund labels it, while different share classes of the same company (GOOG vs. GOOGL) stay separate.
Where the data comes from
Every number on this site starts from an official document, either a fund's SEC filing or the issuer's own published holdings, and flows through the same three steps.
Official Disclosures Only
Holdings are read straight from regulator-mandated or issuer-published documents, never scraped from third-party sites.
SEC N-PORT FilingsQuarterlyMost funds: the portfolio disclosure every US ETF is legally required to file.
Issuer Holdings FilesDailyState Street (SPDR) funds: holdings published by the fund company itself.
Matched and Cleaned
Every position is matched by its CUSIP security ID, and cash, derivatives, and other non-stock positions are set aside.
Rebuilt Nightly
Overlaps, sector breakdowns, and performance are recomputed every night, and every page shows the exact date its holdings are from.
Frequently Asked Questions
The Math
What is ETF overlap?
ETF overlap tells you how much two funds own the same stocks. If overlap is high, buying both funds mostly doubles up on the same companies instead of diversifying. 100% means the two portfolios are identical; 0% means they share nothing.
How is the overlap percentage calculated?
For each stock both funds own, we take the smaller of its two portfolio weights, then add those up. If one fund has 7% in Apple and the other has 5%, Apple contributes 5 points of overlap. This is the same method institutional fund-comparison tools use. We also show how many holdings the funds share and how much of each portfolio sits in those shared names.
Are GOOG and GOOGL treated as the same holding?
No. They are different share classes of Alphabet with different security IDs, so they don't match each other. Index providers and other overlap tools treat share classes the same way.
What is excluded from the calculation?
Cash, money-market instruments, derivatives (futures, forwards, swaps), and negative positions such as currency forwards or collateral offsets are left out. They're operational plumbing, not stock exposure. For nearly all equity ETFs this excluded slice is tiny.
The Data
Where does the holdings data come from?
Official sources only. For most funds we read the fund's latest N-PORT filing with the SEC, the portfolio disclosure every US ETF is legally required to make. For State Street (SPDR) funds we use the issuer's own daily holdings files. Each fund's page shows the exact date its holdings are from.
How fresh is the data?
SPDR funds update daily. Funds sourced from SEC filings update on the SEC's quarterly cycle, so their snapshot is typically two to four months old. That matters less than it sounds: index funds change their holdings slowly, so overlap figures barely move between snapshots. When two funds' snapshot dates are far apart, we flag it on the page.
Where does performance data come from?
Trailing returns are computed from dividend-adjusted daily closing prices, refreshed nightly. 1-month, year-to-date, and 1-year figures are total returns over the period; 3-year and 5-year figures are annualized. Treat them as estimates for comparison; for official numbers, check the fund issuer. Past performance doesn't predict future results.
Where do the sector breakdowns come from?
We classify each underlying stock into GICS-style sectors using issuer fund data plus our own research, then weight by the fund's actual holdings. This is our classification of the portfolio, not the issuer's published sector chart, so figures can differ slightly from the fund company's website. Weight we cannot classify is shown separately as "Unclassified" rather than silently assigned to a sector, and we hide the section entirely when coverage is too low to be representative.
Where does the net-assets figure come from?
Fund size is the ETF share class's assets under management from market data, refreshed nightly. When that's unavailable we fall back to the fund-level total from SEC filings and say so. For funds with both ETF and mutual-fund share classes (many Vanguard funds), the SEC figure covers all classes combined.
Fund Coverage
Why isn't every ETF covered?
There are several thousand US-listed ETFs; we currently track 504 of the most widely held ones. Each fund is onboarded by hand: matched to the right SEC filings, checked for identifier quirks, and spot-checked against the issuer's own numbers. We'd rather cover fewer funds accurately than every fund carelessly, so coverage grows in batches. A fund that's missing today may well be added in a future update.
About this site
ETF Overlap is built and maintained independently. It is not affiliated with, sponsored by, or endorsed by any fund issuer, and nothing here is investment advice.
Found something that looks wrong? Run the comparison and check the as-of dates first. Most apparent discrepancies are snapshot-timing differences.