SPY overlap analysis compares holdings with other ETFs to identify shared positions. Overlapping holdings can lead to unintended concentration risk in a portfolio.

SPY portfolio overlap matters because owning multiple funds with the same underlying stocks reduces true diversification. With 504 holdings, SPY may share significant positions with broad-market funds.

SPY overlap tool lets you enter any other ETF ticker and see the exact overlap percentage and shared holdings. SPY tax-loss harvesting finds highly correlated but non-identical funds.