First principal of TaxLaw: It is all income unless it isn't. It is always taxable unless you can find language in the code exempting it. I'd go a little further in saying that the taxable amount isn't "Y-X", ie the profit. The taxable amount is actually just Y, the sale price. Income is all money literally coming into you. You then need to find a deduction for X, the cost of purchasing the asset. Maybe you find one, or maybe you bought your bitcoins with cocaine and so owe on tax on the entire sale price. Or maybe you have already deducted that cost in a previous year and so cannot deduct it again now. Or maybe you traded your bitcoins for some other bitcoins last year, realized the gain then, and now have to start reviewing the like-kind exchange rules. (I'm in that 0,01% of people who actually enjoy tax law. It's actually very eloquent.)