Pick two funds. We'll show you how much they actually share — by weight, not just by ticker count — so "diversifying" doesn't quietly turn into buying Apple, Microsoft, and Nvidia three times.
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"Shared" is the weight that lands in the same names in both funds. Higher = more of your money doing the same job twice. How much of my money is doing the same job twice?
Under 25% overlap is genuine diversification — you're buying meaningfully different things. 25–60% means there's real redundancy: some of your "second" ETF is just buying what your first ETF already owns. Over 60%? You're effectively holding one fund in a trench coat.
The classic trap: VOO + VTI + QQQ feels like three funds, but they share most of their top-10 holdings — which means your top-10 holdings just got 2-3× the concentration you thought.
The formula, for the formula-curious: Overlap % = Σ min(wA, wB) ÷ min(ΣA, ΣB)
Heads up: this tool uses the top ~25 holdings of each fund (approximate weights from recent public filings) and normalizes against those. It's a directional gut-check, not a portfolio audit — real funds hold hundreds of names whose weights shift daily. Nothing here is investment advice.