Unspent Transaction Output (UTXO)

An unspent transaction output (UTXO) is a discrete amount of bitcoin locked to spending conditions and not yet consumed by any subsequent transaction. Bitcoin has no account balances at the protocol level: a wallet's balance is simply the sum of the UTXOs its keys control, and the complete set of UTXOs, well over 100 million entries, is the network's entire financial state.

How it works

Transactions consume UTXOs whole and mint new ones, so paying 0.3 BTC from a 1 BTC output creates two outputs, 0.3 to the recipient and roughly 0.7 back to the sender as change, minus fees. The model differs deliberately from the account balances used by banks and by Ethereum: since each UTXO is independent, transactions touching different coins can be validated in parallel, and a node can audit the total money supply by summing one data set. The command gettxoutsetinfo in Bitcoin Core does exactly that, letting anyone confirm the circulating supply in minutes. Wallets practice coin selection, choosing which UTXOs to spend, which affects fees and privacy.

In the gold vs bitcoin debate

UTXOs make bitcoin behave like coins rather than like a bank ledger, as each output is a distinct object passed from holder to holder, the digital descendant of a gold piece changing hands. The decisive difference is auditability at scale: proving how much gold exists requires trusting mine records, vault attestations, and estimates, while proving how much bitcoin exists is a computation any node performs against its own copy of the UTXO set.