What to do? Roboadvisor has underperformed the S&P500 by 12.5%

That's unfortunate! Looking at the chart, it seems as if Betterment's system excels at giving you 100% participation in each market decline, offset by about 70% participation in each advance.

Yikes! That's like playing cards at a casino poker table with a big house rake. The pattern is so consistent that it looks as if it's a built-in feature of their model, whether they know it or not.

It's hard for me to imagine any reason to keep more than lunch money in such an account. I can understand the desire, out of sheer intellectual curiosity, to see how the system works. But their product right now looks inferior to a much simpler buy-and-hold approach, based on a relatively static asset allocation that you determine yourself.

There's also fair amount of financial history of can't-miss algorithmic investing that didn't work out, after all. Two examples that come to mind are portfolio insurance (1987) and Long-Term Capital Management (1998.)