Let’s say you bought a Bitcoin for $200 a few months ago and then used it to buy some shares on Angel List today at its current value $448.60 (according to http://preev.com/).
Here’s the problem. That transaction may have resulted in a taxable capital gain to you of $248.60 according to a new IRS ruling taxed at a typical rate of 15%.
The IRS has taken the position that Bitcoins are NOT currency because they are not recognized as legal tender by any country. Instead, the IRS views them as property. When you buy a Bitcoin, that price will be your “cost basis.” When you sell that capital asset, you will either have a capital loss or gain (long term if you held it for a year or more).
When you sell the securities you bought, you will also have a capital transaction that could be taxable. And if you sell them for Bitcoins, you may have a third capital transaction.