Portfolio Overlap Detector
Holding several ETFs feels diversified. Often it isn't. Pick two funds and see exactly how much of their holdings, and their weight, is the same bet made twice.
At a glance
| Tool | Portfolio Overlap Detector |
|---|---|
| What it does | Weight overlap between any two funds in the universe. Number of holdings the two funds share. The ten shared positions that weigh most in both. Excel and PDF export. |
| Universe | Ten widely held US-listed ETFs: SPY, IVV, VOO, QQQ, DIA, VTI, XLK, XLF, XLE and IWM. |
| Data source | Fund holdings and weights from a daily-refreshed cache. The tool returns derived metrics only, never a full holdings table. |
| Price | Free. No account and no sign-in. |
Two funds, one position
Holding several funds is not the same as being diversified. Two broad US equity funds can share most of their weight, because both track a capitalisation-weighted universe and the same handful of companies sits at the top of both. The investor holds two lines in a statement and one exposure in reality.
The problem is invisible from the fund names. Nothing in "large cap blend" and "total market" tells you how much of the second is already inside the first. It only becomes visible when the two holdings tables are put side by side and the shared weight is added up, which is a tedious thing to do by hand and takes seconds here.
How overlap is measured
The tool uses weight overlap, the standard measure: for every security held by both funds, it takes the smaller of the two weights, and sums those minimums across all shared holdings. The result is the share of a portfolio that is genuinely duplicated rather than merely present in both lists.
Taking the minimum matters. A stock at 7 % in one fund and 0.3 % in the other contributes 0.3 %, not 7 % and not the average: only 0.3 % of the two portfolios is truly the same bet. Counting shared tickers instead would report the two funds as nearly identical when one of them barely holds the name at all.
Alongside the percentage, the tool reports how many holdings the two funds have in common and the ten shared positions carrying the most weight in both. Those ten usually explain most of the overlap, and they are the names to look at first if the number comes back higher than expected.
Reading the number honestly
Overlap is a statement about composition, not about correlation. Two funds with low overlap can still move together, because they hold different names with the same drivers. Two funds with high overlap will almost certainly move together, which is the useful direction of the inference.
The figure also depends on the reporting date of the underlying holdings. Funds publish on their own schedules, and a comparison mixing two publication dates carries that difference. The tool reads from a daily-refreshed cache and returns only the derived metrics, never the raw tables.
The universe is deliberately small and widely held rather than exhaustive. Ten funds that many portfolios actually contain answer the question more often than a long list nobody holds.
Questions
- How is the overlap percentage calculated?
- For each security held by both funds the tool takes the smaller of the two weights, then sums those minimums. That is the share of the portfolio that is duplicated rather than simply present in both.
- Which funds can I compare?
- Ten widely held US-listed ETFs: SPY, IVV, VOO, QQQ, DIA, VTI, XLK, XLF, XLE and IWM. Any two of them, in either order.
- Does a low overlap mean the two funds are uncorrelated?
- No. Overlap describes shared holdings, not shared behaviour. Two funds can hold different names and still move together because those names respond to the same drivers.
EPTA5 publishes data and research tools. Nothing on this page is investment advice, a recommendation, or a solicitation to buy or sell any financial instrument. Past performance does not predict future returns.