To compare three of the most popular cryptocurrencies, Bitcoin has a total supply of 21 million, XRP (formerly ripple) has a total supply of 100 billion, but just under half of them are in circulation, and Ethereum (ETH) has no supply limit, with over 110 million already in circulation. The Bitcoin blockchain is designed around the principle of controlled supply, meaning that only a fixed number of new Bitcoin can be minted each year until a total of 21 million coins have been minted. Bitcoin miners will be able to continue earning block rewards until a total of 21 million BTC have been minted, after which no new Bitcoin will enter circulation. There is no real limit to the total number of ETH that can be minted, as with Bitcoin.
Since a new block is added to the Bitcoin block chain approximately every 10 minutes, the total number of Bitcoins in circulation increases by 6.Taking all this into account, the actual number of Bitcoins in circulation today is much smaller than the total number of Bitcoins minted. Once the 21 million Bitcoins have been minted, Bitcoin miners will still be able to participate in the block discovery process, but they will not be incentivised in the form of a reward for Bitcoin blocks. Still, author and Bitcoin advocate Andreas Antonopoulos stressed that the governance drama surrounding the Bitcoin supply cap is not something to lose sleep over, especially since Bitcoin's transition to a purely transaction-based reward model will take 120 years. New Bitcoins are created through a process called mining, which verifies Bitcoin transactions and adds them to the blocks of the Bitcoin blockchain.
It is worth mentioning that even after the last Bitcoin is mined, mining will not necessarily stop, as the reward for mining (and, consequently, for keeping the Bitcoin network operational) will continue to exist in the form of fees for transactions included in the block. It is true that moving to a reward structure based purely on transaction fees would almost certainly decimate the mining network now, as few Bitcoin miners could mine profitably if they received only 6.When Bitcoin mining started, the block reward was 50 BTC per block, but each bitcoin was only worth pennies. While the 18th million bitcoins may not be the best reminder of the current reality of a limited supply cap, the next milestone on the bitcoin horizon will be. It is impossible to know an exact figure, as a lost bitcoin looks exactly the same on the blockchain as one that has not been lost.