There will only ever be 21 million Bitcoins. That's it. Once they're all mined, which should occur in around 2140, no new Bitcoins will enter circulation. The Bitcoin blockchain was designed around the principle of controlled supply, which means only a fixed number of newly minted Bitcoin can be mined each year until a total of 21 million coins have been minted. Once all 21 million BTC have been mined, the network will largely operate the same as it does now, but with one crucial difference for miners. Approximately every ten minutes, Bitcoin miners "discover" a new block, solving a cryptographic puzzle that allows the successful miner to add the newly discovered block to the blockchain. Each block comprises a bundle of transaction records that were previously waiting in the Bitcoin memory pool, usually chosen based on the size of the transaction fee they provide to miners. In return for discovering a block, the miner receives a fixed number of Bitcoins for their work, called the "block reward." When Bitcoin first launched, the reward was set at 50 BTC-but the reward halves every 210,000 new blocks, which ends up being roughly every four years. Thus over time, the block reward has been cut to 25 BTC, 12.5 BTC, and 6.25 BTC. Three halvings have been completed so far; the most recent Bitcoin halving occurred in May 2020, cutting the block reward to 6.25 BTC. The next halving is expected to occur in 2024. Bitcoin miners will be able to continue earning block rewards until a total of 21 million BTC has been minted, after which no new Bitcoin will enter circulation. Currently, just over 18.5 million BTC has been produced, equivalent to 88.3% of the maximum supply, minted in just over a decade. But it will take another 120 years before the last Bitcoin is minted, due to the gradual reduction of new Bitcoin creation caused by the halving process.

Once all 21 million Bitcoin have been minted, Bitcoin miners will still be able to participate in the block discovery process, but they won't be incentivized in the form of a Bitcoin block reward. That's not to say they won't be rewarded at all, though. As well as block rewards, Bitcoin miners also receive all the fees spent on the transactions included in each newly discovered block. Currently, transaction fees make up a small proportion of a miner's revenues, since miners currently mint around 900 BTC (~$39.8 million) a day, but earn between 60 and 100 BTC ($2.6 million to $4.4 million) in transaction fees each day. That means transaction fees currently make up as little as 6.5% of a miner's revenue-but in 2140, that'll shoot up to 100%.

It's true that switching to a reward structure based purely on transaction fees would almost certainly decimate the mining network now, since few Bitcoin miners would be able to profitably mine Bitcoin if they received just 6.5% of their typical rewards. However, if the usage of the Bitcoin network were to explode, then competition for block space could increase dramatically. According to ByBit CEO Ben Zhou, that would likely lead to increased transaction fee rewards for miners-similar to what was seen during Bitcoin's 2017 bull run. At its peak in December 2017, the total transaction fees paid per day spiked to 1,495 BTC at a time when Bitcoin was valued at $14,000. As a result, miners earned a total of $21 million in transaction fees that day-which is currently around half of what they earn from the block reward today, indicating that something similar could occur in the future.

Obviously, if a majority of miners-or even all miners-stopped mining Bitcoin, then the Bitcoin network would, in many ways, change forever. You would still be able to view which wallet addresses hold Bitcoin, and how much,, and you would also still be able to view the entire history of every single Bitcoin transaction ever made. But confirming new transactions requires mining. If miners stop producing new blocks, it would effectively become impossible to spend any Bitcoin in the future. That's quite the doomsday warning for the Bitcoin network, but many believe miners will stay the course, even once transaction fees are their only reward. And as #Hashed CEO Simon Kim told Decrypt, there may be changes down the line that can incentivize miners even if block rewards stop, but not everybody agrees.