Bitcoin is similar to gold in several ways. Gold is mined out of the ground while Bitcoin is mined through digital means. With the stipulation set by the founders of Bitcoin, similar to gold, it has a limited supply. There are only 21 million Bitcoins that can be mined in total.
January 13, 2018, marked as an important milestone for Bitcoin, was when 16.8 million Bitcoins were mined - that was 80% of the entire Bitcoin supply. This means that only 4.2 million Bitcoins or 20% are left to be mined until the 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 have been mined. It is estimated that this will happen in the year 2140.
Interested in buying Bitcoin? Check the market now: https://www.bitkub.com/market/BTC