Easy, only what you can afford to lose. We'll always get back to that short phrase about investing tip in bitcoin. One must invest in bitcoin with the amount that he's not going to be stressful and okay to be seeing it at a dramatic loss. Because of the market isn't stable and it's always have been volatile, if you ever invest on it then you have to make sure that you're not just here for the quick profits and you're willing to wait as if you're waiting for something big and that might take a long time. We holders have learned that the hardest ways but you know what's best with that? It's been rewarding and that every single year of waiting is definitely worth the wait as if you're waiting for the love of your life.