max supply

Bitcoin's maximum supply is capped at 21 million coins. This limit is not a policy that can be changed by a committee or a central bank. It is written directly into the protocol and enforced by every node on the network. Any attempt to issue bitcoin beyond this limit would produce a block that every validating node would reject. The cap has been in place since Bitcoin launched in 2009 and has never been altered.

New bitcoin enters circulation only through the block reward, a fixed amount of bitcoin given to the miner who successfully adds a new block to the blockchain. This reward started at 50 bitcoin per block and is cut in half approximately every four years in an event called the halving. The halvings continue until the reward becomes so small that it effectively reaches zero, which is projected to happen around the year 2140. At that point, the total supply in circulation will approach but never quite reach 21 million due to the way the halving schedule compounds over time. A small number of coins are also permanently lost through forgotten keys and other circumstances, meaning the effectively circulating supply is somewhat below the theoretical maximum.

The fixed supply is often cited as one of the properties that distinguishes bitcoin from traditional currencies. Central banks can expand the money supply of fiat currencies at any time, which tends to dilute the purchasing power of existing holders over time. Bitcoin's protocol makes this kind of dilution impossible. The relationship between fixed supply and inflation is central to many arguments made in favour of bitcoin as a long-term store of value: if demand grows while supply remains fixed, the purchasing power of each unit tends to rise rather than fall.