Coinbase Transaction

Overview

Every valid Bitcoin block contains exactly one coinbase transaction, placed first in the block’s transaction list. The transaction creates new bitcoin according to the current subsidy schedule and claims fees from the block’s other transactions. The total output value cannot exceed the permitted subsidy plus fees.

The coinbase input uses a null previous-output reference because there is no earlier UTXO being spent. It also includes the block height and can contain extra data selected by the miner. Miners often use part of this field to vary the block header search space.

Outputs from the coinbase transaction must mature for 100 additional blocks before they can be spent. This rule prevents miners from spending rewards from a block that is later removed in a reorganization.

The term should not be confused with the cryptocurrency exchange named Coinbase. It is a Bitcoin protocol concept that existed before the company. Other blockchains may distribute validator rewards through different system operations and may not use a Bitcoin-style coinbase transaction.

The transaction also commits to data used by mining pools, including payout arrangements or auxiliary information. Because it has no ordinary sender, explorers display its input differently from standard transactions. The reward can be divided among several outputs, such as a pool and its participants. Developers parsing Bitcoin blocks should explicitly recognize coinbase transactions rather than applying normal input-value logic, because the created value comes from consensus rules instead of previous outputs.

The transaction is also part of the block’s Merkle tree like other transactions. Any change to its outputs or data changes the Merkle root and therefore the header hash, allowing miners to search additional candidate block hashes.