There is no minimum investment at Betterment, and no minimum balance. 

One reason we have no minimum balance is to ensure that every investor can get started building wealth with both long-term and short-term goals.

Betterment is a powerful way to put idle balances to work for you, including your safety net fund. Americans on average do not save nearly enough money, so we challenge you to deposit as much as you can comfortably afford because the more you invest the more that will grow. Note that the amount Betterment charges depends on your account balance. For more detail, look at our pricing page