In the context of income tax, capital gains from the purchase and sale of cryptocurrencies are to be declared.
Case 1 : capital gain following the sale of cryptocurrencies in euros ; gain = sale price - purchase price. Please note that losses are not declared.
Case 2 : capital gain following the purchase of goods in cryptocurrencies ; gain = euro equivalent of the goods - purchase price of the cryptocurrency.
In the context of wealth tax, the cryptocurrency stock must be declared on 1 January (at the exchange rate as of 1 January).