Throughout 2017, the number of bitcoin in circulation increased from about 16 million to 17 million, but it will slow down as it gets closer to the 21 million limit. (finder.com)
But with more bitcoins in circulation, people also expect transaction fees to rise, possibly making up the difference. (businessinsider.com)
That number is calculated by the number of bitcoin in circulation multiplied by the price per coin. (cryptonews.com)