Robo-advisors are novel tools in financial markets that provide investors with low-cost financial advice, usually based on individual characteristics like risk attitudes. We study the benefits of robo-advice in a portfolio choice experiment running over ten weeks. Depending on treatment, investors either receive robo-advice, have a robo-advisor implementing recommendations by default, or have to invest on their own. While we observe no effect of robo-advice on initial market participation, we do find positive effects on continued market participation. Robos also help investors avoid mistakes, make rebalancing more frequent, and overall yield portfolios much closer to the utility maximizing ones. Robo-advisors that implement the recommendations by default do significantly better than those that just give advice.