Fidelity 500 index fund return rate July 8, 2019 16 32 64 128 Fidelity s&p 500 index fund return rate Fidelity 500 index fund rate of return history Fidelity 500 index fund fxaix rate of return Fidelity s&p 500 index fund Fidelity 500 index fund Index funds Fidelity index funds