Digital coins are created each time a user discovers a new block. The rate of block creation is adjusted every 2016 blocks to aim for a constant two-week adjustment period (equivalent to 6 per hour.) The number of Bitcoins generated per block is set to decrease geometrically, with a 50% reduction every 210,000 blocks, or approximately four years. The result is that the number of bitcoins in existence will not exceed slightly less than 21 million.
Bitcoin’s blockchain protocol makes mining more difficult as more miners join the pool, and the crypto reward for mining a block also halves every 210,000 blocks. As it stands, miners receive a 12.5 BTC reward for unlocking a new block. The next reward halving will happen in May 2020 – reducing the reward to 6.25 coins.
When will bitcoin run out? If the mining power had remained constant since the first Bitcoin was mined, the last coin would have been mined somewhere near October 8th, 2140. Due to the mining power having increased overall over time, as of block 367,500 – assuming mining power remained constant from that block forward – the last BTC will be mined on May 7th, 2140. As it is very difficult to predict how mining power will evolve into the future, putting an exact date or even year on this event is difficult.