Total number of Bitcoins in circulation
The total supply of Bitcoin is limited and pre-defined within the Bitcoin protocol at 21 million, with the mining reward (how Bitcoins are created) decreasing over time as supply reaches it's limit. Mining rewards are decreased due to Bitcoin halving events taking place. Halving events reduce the reward that miners get when successfully mining new Bitcoin blocks. The chart below shows how many Bitcoins have already been mined or put into circulation.
Bitcoin AI
Bitcoin supply — Bitcoin AI can explain issuance and the 21M cap.