I recal a thread on /r/personalfinance where someone bought Bitcoin, directly for another altcoin after the Bitcoin value went up, the end-of-year happened, the

I recal a thread on /r/personalfinance where someone bought Bitcoin, directly for another altcoin after the Bitcoin value went up, the end-of-year happened, then in January the altcoin value tanked. If both happened in the same year that person could use the loss of the altcoin to offset the gain of the bitcoin. But since they were in separate years, they had to come up with some huge amount of money to pay taxes on the gains from bitcoin (gains that were wiped out by the drop in value from the altcoin). To do this properly, everytime you use bitcoin to buy something you should sell enough bitcoin (for cash) at the same time to generate enough cash to cover the tax on the main transaction (assuming bitcoin went up in value from when you acquired it).