A good starting place for most investors looking at index funds for their Roth IRAs are low-cost broad-based stock or bond index funds. Cost should be a major determining factor for investors looking at long-term investment options. For the stock fund, investors might consider the Fidelity ZERO Total Market Index (FZROX) fund, a low-cost U.S. stock index fund, or the Fidelity ZERO International Index (FZILX) fund, a low-cost international stock index fund. For the bond fund, investors may consider the Fidelity U.S. Bond Index (FXNAX) fund, a low-cost bond index fund.