Wow! Fidelity's ZERO (no-fee) index funds bring in $1B in first first month. That's a lot of money. Should you switch? Maybe. But, probably not. If you are already using low-cost passively managed index funds, the move to Fidelity might only save you $4 per $10,000 invested - not exactly a King's ransom. For example, many passively managed index funds already have an expense ratio of .03% to .05%; as such, a $10,000 investment already only costs about $3 to $5 per year. Now if it turns out that Fidelity's "tracking error" of its bogey benchmark is less effective than other funds, then Fidelity's ZERO funds could actually end up costing you more in lost returns (albeit, not a huge sum most likely). Additionally, Fidelity seems to admit that these ZERO funds are a loss leader for them. Accordingly, they will need to recoup these fees by cross-selling additional products to these new customers. Finally, if you are considering switching a taxable account to Fidelity's ZERO funds, such an event can trigger a capital gains tax event and a corresponding tax bill from Uncle Sam (something most of us don't want). Nevertheless, Fidelity's ZERO funds are really good news for the average investor because reducing costs is one of the best things an investor can do to boost their returns!