Verkkoi swapped over from a mix of target date funds and mutual funds, to a pure 100% fxaix (fidelity’s s&p tracker) portfolio at the end of 2021, at the absolute peak right before. Which index fund will reign supreme? Learn the key differences between these popular funds and find out which one is best for your. Verkkothe fxaix fund invests at least 80% of its assets in stocks included in the s&p 500 index, aiming to closely track the index's performance.