Coinbase Transaction

A coinbase transaction is the first transaction in every bitcoin block, created by the miner to collect the block reward. It has no inputs: it mints the block subsidy, 3.125 BTC since the April 2024 halving, and gathers the fees from every transaction in the block. Its outputs cannot be spent until 100 blocks later.

Why it matters

The coinbase transaction is the only way new bitcoin comes into existence, which makes it the enforcement point of the 21 million coin supply schedule. Every full node checks that a block's coinbase claims no more than the permitted subsidy plus fees, so a miner attempting to overpay itself produces an invalid block that the network simply discards. The term predates and has nothing to do with the exchange of the same name, which borrowed it.

How it works

The subsidy halves every 210,000 blocks, roughly every four years, stepping from 50 BTC in 2009 down to zero around the year 2140, after which fees alone will pay miners. The coinbase also contains a small free-form field where miners embed data, famously the newspaper headline Satoshi placed in the first block in January 2009. The 100-block maturity rule exists because a chain reorganization could erase a recent block and its reward, so newly minted coins must age before they can be spent.