Bitcoin is similar to gold in several ways. Gold is mined out of the ground while Bitcoin is to be mined through digital means. With the stipulation set by the founders of Bitcoin, similar to gold, it will have a limited supply. There are only 21 million Bitcoins that can be mined in total.
Last January 13, 2018, marked an important milestone for Bitcoin when 16.8 million bitcoins were mined - that’s 80% of the entire Bitcoin supply. This means that only 4.2 million bitcoins or 20% are left to mine until 21 million bitcoin supply cap is reached. Bitcoin protocol requires that the mining reward is halved every 210,000 blocks. Blocks take about 10 minutes on average to mine, halvings occur about every 4 years. After 64 total halvings, all 21 million Bitcoins will be mined. It is estimated that this will happen in the year 2140.