This leaves less than three million that have not yet been put into circulation. To explain, due to a stipulation embedded in its source code, there can only be 21 million bitcoins mined. That seems like a lot, but in the last decade 18.So you would think that when they get to 21 million that's going to cause some problems. Once 21 million BTC have been mined, the network will function largely the same as it does now, but with one crucial difference for the miners. Since bitcoins can only be created by being mined, all bitcoins in existence are bitcoins that have been mined.
Let's look at the details of how many bitcoins have been mined, the future of the bitcoin market and what this means for investors. Once all the bitcoins have been mined, miners will continue to receive transaction fees as an incentive to keep their equipment running. Similarly, if all the bitcoins were mined within a few years, enthusiasm for the cryptocurrency could die out quickly, and it would not have a chance to build itself as a viable industry and currency. That is, in about 120 years' time, in the year 2140, nodes will have effectively mined the 21 million bitcoins reaching the maximum supply. The Bitcoin blockchain was designed around the principle of controlled supply, which means that only a fixed number of new Bitcoins can be minted each year until a total of 21 million coins have been minted.
This means that, at the current rate, the last bitcoin will not be minted until 2140, and that is a long time in which protocols could change and thus there could be a greater supply. Another possibility is that Bitcoin's reward mechanism will change some time before the last block is mined. Even so, when the time comes and all the bitcoin has been mined, it seems that it will be the miners who will be most affected, as once there is no more to mine they will be forced to give up due to the lack of rewards - or bitcoin - they would receive for mining a block. While gold must be mined from the physical earth, bitcoin must be mined by computational means. While it is true that the vast majority of bitcoin has already been mined, the timeline is more complicated than that.
In reality, as the year 2140 approaches, miners will likely spend years receiving rewards that are really only small portions of the final bitcoin that will be mined.