This is easy. You want a low cost index fund. Vanguard has a number of good ones. The Vanguard Total Stock Market Index Fund is probably the best bet. 0.05% expense ratio for admiral shares, a bit more for investor shares. They're a few others that only cover the S&P 500, or include some bonds, or have more international exposure but at your age and savings level it's not worth agonizing over the differences. Just go with the broadest, lowest cost stock fund you can find.