According to an independent assessment, 43% of revenue was in December alone. Coinbase was one of the first interfaces to make Bitcoin accessible to the masses using credit cards and bank exchanges.
The exchange expected a 600 million profit for 2017 but the bitcoin run in the final weeks of the year nearly doubled that estimate. According to the New York Times, Coinbase was receiving eight times as much traffic in December as it was in June. It makes money from transaction fees. Due to this fact during the high rate of trading that went on from about Thanksgiving through to New Years, the exchange would have seen much higher profits.
However, it is not possible to repeat such success in 2018 unless there is another surge in cryptocurrency trading. Moreover, because of increasing Competition Coinbase may not see the same profits.
Coinbase is going to generate profits with a new merchant platform Coinbase Commerce which will enable vendors to accept cryptocurrencies. It will generate profit from participating merchants while encouraging the growth of cryptocurrency use, garnering fees from those transactions as well.