[saosebastiao]

So any price from any exchange at any time during the day? You haven't clarified a thing by telling me to use the fair market value, because there is no standardized way to determine fair market value. These aren't stable mature markets, a blink of the eye and the market may be transacting at +/-10%. Determining fair market value is the primary problem with cryptocurrency taxation. If you're lucky enough to be trading in USD paired currencies, great...you can use actual transaction values. But the vast majority of crypto trades aren't with any fiat pair.

[s73v3r_]

The fact that these things are extremely volatile is not the IRS's problem. You are the one responsible for recording the details of your trade.

[saosebastiao]

I did record the details of my trade. What I didn't record was the concurrent status and details of some completely unrelated market on a completely unrelated exchange that establishes some sort of mythical fair market value denominated in USD that so far has no canonical way of being calculated anyway. Nobody can answer the question in any precise way, the IRS guidance on the issue is barebones and not informative at all, and my CPA can't figure it out either. The best we can do is take a best guess that makes it look like I'm not stiffing the IRS.

I want to pay my taxes. I believe crypto should be taxed. But when you get into the situation where well meaning people have to take guesses at what is appropriate, and differences between seemingly simple rules of thumb can result in 20+% disparities in taxes owed, you're gonna have a bad time no matter how diligent you are.