Playing Devils advocate here. Where do you get the value of bitcoin at time your trade is made? Since bitcoin can vary by a hundred or more
That is a problem for which I'm pretty sure there's no official IRS answer. I downloaded daily Bitcoin prices (I think from Quandl) and used those. Since the IRS doesn't provide guidance for this I would hope that I'm ok as long as I use a consistent source and don't cherrypick the Bitcoin values.