When you count your income from mining, you need to create an equal cost basis at that time. The value of the coins when you received them is your cost basis. I

When you count your income from mining, you need to create an equal cost basis at that time. The value of the coins when you received them is your cost basis. If you didn't do that, you paid way too much in taxes. (If you hold them for longer than a year before you sell them, you can be paying long-term capital gains which is cheaper than short-term. Unless you're in losses in which case it doesn't matter.)