If I have money now, I would buy half of bitcoin because in next three months it will double the current price. This is real because it always occur this way after 5 years remember in 2011 and 2017 from the market charts and caps. And this year will break more even.
What makes you so sure that the price will be doubled in the next three months? It's been 3 months already since you created this thread, yet the price didn't moved and doubled just like the way you expected it to be or at least speculated because from the month of March until today, bitcoin's price has only increased in about more or less $3,200.
But what you said was right because it seems that buying cheap is actually the best formula and as long as you know the right target (coin), then there's a good chance that your assets will double soon enough.
Everyone knows that buying low and selling high is a recipe for profit in this market, but what is called cheap? As you said, if OP's formula is the best, why has it been 3 months, and he still hasn't made a significant profit?
Bitcoin is suitable as a long term investment, so accumulate it as much as possible and the best time to buy is when we have money to invest and are ready to hold it for long until it generates profit for us.
In my opinion, in the market, there is no general formula to generate profits, each investor will have his own formula drawn from knowledge and experience.