If you receive forked tokens as a result of a hard fork of a blockchain on which you already have tokens, the receipt of the forked tokens is tax-free. However, there is a tax liability on the sale of the forked tokens.
The calculation method is the same as for spot trades.
For example, if you have 10 ABC1 tokens in your wallet and receive 10 ABC2 tokens in your wallet because the ABC1 blockchain is forked, the receipt of the 10 ABC2 tokens is tax-free. This is because the tax authorities consider that you already acquired the 10 ABC2 tokens when you acquired the 10 ABC1 tokens.
The acquisition cost for your 10 ABC2 tokens was 0 kr. When you sell your 10 ABC2 tokens for a value of 10,000 DKK, you must report the full profit (10,000 DKK) as other personal income (box 20).