One of the chief characteristics of Bitcoin (BTCUSD) is that its coin supply is limited. Bitcoin inventor Satoshi Nakamoto, the anonymous name used by the creators of the Bitcoin cryptocurrency, designed the cryptocurrency essentially as digital gold and capped the Bitcoin maximum supply to mimic the finite quantity of physical gold.
The maximum number of bitcoins that can be issued—mined—is 21 million. New bitcoins are added to the Bitcoin supply approximately every 10 minutes, which is the average amount of time that it takes to create a new block of Bitcoin.1 By design, the number of bitcoins minted per block is reduced by 50% after every 210,000 blocks, or about once every four years.
The total number of bitcoins issued is not expected to reach 21 million. That’s because the Bitcoin network uses bit-shift operators—arithmetic operators that round some decimal points down to the closest smallest integer.2
This rounding down may occur when the block reward for producing a new Bitcoin block is divided in half, and the amount of the new reward is calculated. That reward can be expressed in satoshis, with one satoshi equaling 0.00000001 bitcoins.1 Because a satoshi is the smallest unit of measurement in the Bitcoin network, it cannot be split in half. The Bitcoin blockchain, when tasked with splitting a satoshi in half to calculate a new reward amount, is programmed—using bit-shift operators—to round down to the nearest whole integer.2 This systematic rounding down of Bitcoin block rewards, in fractions of satoshis, is why the total number of bitcoins issued is likely to fall slightly short of 21 million.
As of January 2022, 18.9 million bitcoins have already been issued, with about 2.1 million bitcoins still to be released.3
With the number of new bitcoins issued per block decreasing by half approximately every four years, the final bitcoin is not expected to be generated until the year 2140. The number of new bitcoins minted per block was 50 when Bitcoin was first established, and has since decreased to 6.25 as of May 2020.
Although a maximum of 21 million bitcoins can be minted, it’s likely that the number of bitcoins circulating remains substantially below that number. Bitcoin holders can lose access to their bitcoins, such as by losing the private keys to their Bitcoin wallets or passing away without sharing their wallet details. A June 2020 study by the crypto forensics firm Chainalysis estimates that up to 20% of the Bitcoin already issued may be permanently lost.4
After the maximum number of bitcoins is reached, even if that number is ultimately slightly below 21 million, no new bitcoins will be issued. Bitcoin transactions will continue to be pooled into blocks and processed, and Bitcoin miners will continue to be rewarded, but likely only with transaction processing fees.1
Bitcoin reaching its upper supply limit is likely to affect Bitcoin miners, but how they are affected depends in part on how Bitcoin evolves as a cryptocurrency. If the Bitcoin blockchain in 2140 processes many transactions, then Bitcoin miners may still be able to generate profits from only transaction processing fees.
If Bitcoin in 2140 largely serves as a store of value, rather than for daily purchases, then it’s still possible for miners to profit—even with low transaction volumes and the disappearance of block rewards. Miners can charge high transaction fees to process high-value transactions or large batches of transactions, with more efficient “layer 2” blockchains like the Lightning Network working in conjunction with the Bitcoin blockchain to facilitate daily bitcoin spending.
But if Bitcoin mining in the absence of block rewards ceases to be reliably profitable, then some negative outcomes can occur:
Will Bitcoin function like pocket change or bars of gold in the year 2140? The Bitcoin ecosystem is still developing, making it possible if not likely that Bitcoin itself will continue to evolve over the coming decades. But however Bitcoin evolves, no new bitcoins will be released after the 21-million coin limit is reached. Reaching this supply limit is likely to have the biggest impact on Bitcoin miners, but it’s possible that Bitcoin investors could experience negative impacts as well.
As of January 2022, 18.9 million bitcoins have already been mined, with about 2.1 million bitcoins still to be released. The total Bitcoin supply is capped at 21 million.3
The length of time it takes to mine one Bitcoin depends on the amount of the block reward, or how many new Bitcoins are paid to crypto miners for generating a new Bitcoin block. The current block reward is 6.25 Bitcoins, and a new block is produced approximately every 10 minutes. A new bitcoin is mined on average every 1.6 minutes.12
Bitcoin mining fees will disappear when the Bitcoin supply reaches 21 million. Miners will likely earn income only from transaction processing fees, rather than a combination of block rewards and transaction fees.