The Portuguese tax agency has ruled that gains on sales of cryptocurrencies (e.g. bitcoins) are taxed in Portugal only if these transactions are performed on a regular basis and therefore constitute a professional or business activity by the taxpayer. In this case, the gains would be included in category B of the personal income tax (Impuesto sobre la Renta de las Personas Singulares or "IRS").
According to the tax agency, although these kinds of gains could in theory fall within categories G (capital gains) and E (income from capital), this does not ring true given that virtual currencies are not a financial derivative product or a transferable security, nor do they derive from a mere investment of money.
This ruling was issued under binding ruling process no. 5717/2015, within which clarifications were requested on the treatment of this kind of income for personal income tax purposes.