Free tool
Overlap checker
Two funds can look different and hold the same companies. Enter two tickers to see how much of their weight is the same, which positions they share, and how recent the underlying holdings files are.
Try VOO and QQQ, SCHD and VYM, or QQQ and QQQM. Runs in your browser; nothing you type leaves the page.
Why published overlap figures disagree
Search for the overlap between two well known funds and you will find four different numbers on four sites. They are not errors. They are different measures, quoted without saying which one, and often computed from holdings files months apart.
This tool shows all three at once, and prints the publication date of each fund's holdings file, so the figure can be checked rather than believed. The definitions are on the methods page.
What overlap does not tell you
A high overlap means two funds own the same companies, not that they will behave identically. Weights matter as much as names: two funds can share every holding and still diverge if one concentrates its top ten positions far more than the other. The comparison pages put the two side by side.