Swedish tax authorities.
Sales and payment with bitcoin
Divestment of assets entails capital gains taxation. By divestment, the sale, exchange and similar transfer of assets. A pure sale of bitcoin in which compensation is received in the form of kronor or foreign currency is thus subject to capital gains tax. Payment with bitcoin when purchasing a product (such as a pair of shoes) or a service (such as a taxi ride) means that bitcoin has been sold for a consideration that corresponds to the value of the item or service. Any such payment with bitcoin therefore entails a separate capital gain calculation.
The cost of each capital gain calculation shall be calculated using the so-called average method. If bitcoin has been acquired on several occasions, you should calculate an average cost amount.
The standard method
If you have no indication of what you bought the shares for, you can use the standard method. Even if you know the actual cost amount, you can use the standard method.
You may use the method, for example, if you have sold market-listed shares or listed stock index bonds. You may not use the method on futures and options, nor on subscriptions, fund shares or redemptions and sales rights that you have obtained as a result of shareholding.
This method means that you use 20 percent of the selling price, after deduction of the bank fee or courtace, as cost. The remaining part, that is 80 per cent of the selling price, is counted as profit.
Note that if your shares increase in value more than 400 percent, it is more preferable to use the standardized method.