21 BTC21 million supply cap
There will never be more than 21 million bitcoins. Over 95% are already issued; the rest trickles out with each block until about 2140.
Short definition
The maximum number of bitcoin that will ever exist, enforced by every node.
Where the number comes from
210,000 blocks × 50 BTC = 10.5 million in the first era, then half as much in each following era: 10.5 + 5.25 + 2.625 + … approaches 21 million. Because the subsidy is rounded down to whole satoshis, the true maximum is about 20,999,999.98 BTC.
Changing the cap would need nearly every node operator to switch to different software; nodes reject blocks that pay more than the rules allow.
Lost coins
Some coins are gone for good: keys thrown away, forgotten or destroyed. Estimates run into millions of BTC; the Hacks page lists the best-known cases and estimates with sources.
See also
- HalvingEvery 210,000 blocks, roughly every four years, the number of new bitcoins paid to miners per block is cut in half. This is how Bitcoin's supply is capped at 21 million.
- Satoshi (unit)A satoshi, or sat, is the smallest amount of bitcoin: one hundred-millionth of a coin. 1 BTC = 100,000,000 sats.
- BitcoinBitcoin is digital money that no company or government runs. Anyone can send it to anyone over the internet, and no one can create more than 21 million coins. The network started on 3 January 2009.
- MiningMining is the work that adds new blocks to Bitcoin. Miners run special computers (ASICs) that guess numbers; the winner of each round earns the block subsidy and the fees.
References
- Bitcoin Wiki: Controlled supply en.bitcoin.it
- Satoshi Nakamoto, Bitcoin: A Peer-to-Peer Electronic Cash System (2008) bitcoin.org