17 million bitcoins have been mined as of April 26, 2018. Only 4 million bitcoins or 19% are left before the 21 million cap is reached.
According to satoshi.info data, the 17 millionth bitcoin was mined on April 26, 2018 at around 9:00 pm – 10:00 pm. The last bitcoin that hit the million mark (16M) was mined in late November 2016.
This 21 million coin cap gives bitcoins an element of scarcity. Because of bitcoin’s protocol, the rate of coins produced gets slower over time. This means that for every 210,000 blocks, the reward for mining bitcoin halves the block reward and this will make BTC creation slow down. The last recorded halving was in July 2016 which rewards miners with 12.5 BTC per block. If the protocol stays the same the last bitcoin is projected to be mined in 2140.
This mining and scarcity are similar to that of precious metals such as gold, which bitcoin is always compared to.