Based from what I know, there are websites like usi-tech that lets you invest your bitcoins for months, and the pay-out is relatively good. The only factor that you must consider is the volatility of its price since the pay-out heavily relies on the price of bitcoins. Let's say that the price today is around $6000 and after 2-3 months it fell to $5500, then you incur a loss on your investment. Nevertheless, if you are going to based it on the price history index of bitcoin prices, then it might be a good idea to invest due to the consistency of the price increases.