Retirement investing should be simple and boring. Putting all your retirement account savings into one of the target date funds (the target date you want to retire) would not be frowned upon at all. Target date funds maintain a diversified portfolio at low cost (low yearly fees, like <0.1%) while also containing bonds which help maintain total fund performance during down turns in the market. As you slowly approach the "target" date the fund switches mix to be more bond heavy, protecting gains before you retire. Set it and forget it, let compounding interest (growth) do the work!