VTI tracks the CRSP US Total Market Index, which covers nearly the entire investable US stock market, roughly 3,500 companies from mega-caps to micro-caps, weighted by market capitalization. Because of cap weighting, the largest companies such as Apple, Microsoft, NVIDIA, Amazon and Alphabet account for a large share of returns. Compared with VOO, VTI adds a few thousand small and mid-cap stocks, which together make up a modest share of total assets. As a result, the long-term performance of VTI and S&P 500 funds has been very similar. VTI and ITOT track the total US market with slightly different indexes and are close substitutes.
