Also don't forget our IRS friends, every time you sell a crypto coin to cash out or buy another, you owe Uncle Sam a big junk of your profits - for a holdings less than a year, more likely equal to your income tax bracket and if you think you are anonymous, think again and consider how likely your exchange is to turn all their records to the US government...
from my understanding, if bitcoin went down 50% based on the value you had invested in the beginning of the year, you pay nothing of taxes, because you had no profit. and you only pay taxes if you sell it.
i frequently trade in the stock market and that's how it works there though.
https://www.cnbc.com/2017/11/30/bitcoin-investors-beware-the...
https://www.bloomberg.com/news/articles/2017-11-16/bitcoin-h...