Advantage Class benefits and requirements differ among various Fidelity index-based mutual funds, including the low-cost Spartan Funds. The Spartan index funds, which already feature lower expense ratios, require a $10,000 minimum investment for Advantage Class shares, and certain other non-Spartan index funds require a $2,500 investment for this class of shares. The expense ratio reductions vary, but they are generally up to approximately 60 percent lower than expenses for regular shares, known as Investor Class shares. For example, at the time of publication, the net expense ratio for Fidelity Spartan Mid Cap Index Fund Investor Class shares was 0.23 percent and the minimum investment was $2,500. In contrast, the fund's Advantage Class shares charged 0.09 percent and required a $10,000 minimum. Advantage Institutional Class shares required a minimum investment of $100 million and offered even lower net expense ratios.