One of the two parties is paying the market-making, the other the market taking fee. So for every transaction, there is always a 0% + 0.3% total commission for

One of the two parties is paying the market-making, the other the market taking fee. So for every transaction, there is always a 0% + 0.3% total commission for Gdax. (note, large customers get a discount on the taker fee, so I went with 0.25% on average)