The circulating coin supply is derived directly from the block height and refers to the amount of Bitcoin in existence. While only 21,000,000 Bitcoin will ever exist, the amount circulating is much lower than that as many Bitcoin have yet to be mined in future blocks. As of 2021, only 18,500,000 Bitcoin exist, with 2,500,000 remain to be mined in the future. This number does not take into account lost Bitcoin, or burned Bitcoin – and in reality the true amount circulating may be much less than the 18.5M BTC figure as well.