What Is a UTXO? Unspent Transaction Output Explained

How UTXOs work

Think of UTXOs like physical bills. If you're paid a 5 coin output and a 2 coin output, your balance is 7, but you hold two separate "bills". To pay someone 6, your wallet must spend both whole outputs (7 total), send 6 to the recipient, and send the remainder — minus the network fee — back to you as a new "change" output.

Each output can only be spent once. When a transaction spends it, it becomes part of history; the new outputs it creates are the fresh unspent ones.

Why UTXOs affect fees

A transaction's size depends on how many outputs it consumes. Spending ten tiny outputs makes a bigger transaction than spending one large output, and fees are usually charged per byte — so a wallet made of many small payouts (typical for miners receiving frequent small rewards) can cost more to spend than the same total held in a few larger outputs.

UTXO vs account model

Ethereum and Solana track balances per account, like a bank ledger: a transfer just decreases one balance and increases another. UTXO chains have no such balance record; wallets calculate your balance by scanning for outputs your keys can spend. Neither is strictly better — UTXOs offer simpler parallel validation and some privacy properties, accounts offer simpler programming.

Practical tips

• Don't panic when a transaction sends "change" to a new address of yours — that's normal
• If you receive lots of small payouts, consolidating them during low-fee periods can save money later
• Expect the wallet, not you, to pick which outputs to spend