There are 2 recommendations to enter coins that forked:


1) The easy way:

Add the new coin as 'gift' or 'income' (depending on the tax laws of your country) with the initial price as cost basis.

For example: adding your BCH after the BTC Fork = add your BCH as 'gift' with a cost basis of 274.59 USD per coin (the initial price on August 1st).


2) The correct way:

To make it 100% tax compliant, you would have to search for every single transaction you made with the old coin and create an additional transaction at the same date/time and with the same amount (just with a 0 USD cost basis) for the new coin.

For example: adding your BCH after the BTC fork = search for every single BTC transaction you made (before August 1st) and create an additional BCH transaction at the same date/time and with the same amount (just with a 0 USD cost basis).


At the end your new coin amount will be the same as your old coin amount.