What is the actual difference between Vanguard VTI and VOO?

Vanguard S&P 500 ETF (VOO) holds approximately 500 large-cap U.S. stocks, while Vanguard Total Stock Market ETF (VTI) holds over 3,600 stocks—encompassing large, mid, small, and micro-cap U.S. companies. Because both funds are market-cap weighted, large-cap companies dominate both holdings: roughly 82% to 85% of VTI is identical to VOO. Historically, their correlation exceeds 0.99 with nearly indistinguishable annualized returns (around 10%), both charging an ultra-low expense ratio of 0.03%. VOO offers slightly less volatility, while VTI provides broader total diversification.