Fees are calculated in terms of each asset traded or transferred on NEX. For example, if a user places a market price order trading 1000 NEX for NEO, then the exchange will collect a fee of 1000 * 0.0025 = 2.5 NEX. Similarly, if a user transfers 1000 NEO on the payment service for a fee of 0.001 GAS, that fee will be added to the GAS fee total. Total NEX fees are calculated by simply computing the fees taken for each asset on the exchange. As fees are taken, a proportion of them are moved to an independent smart contract that manages the claiming process.