UTXO means unspent transaction output. It is an output of an earlier transaction that remains available to spend, subject to its locking conditions. A wallet’s displayed balance is derived from spendable outputs rather than a single account-balance field in the protocol. Transaction documentation.
Follow the change
Consider an illustrative transaction with one input worth 100,000 satoshis:
| Destination | Amount |
|---|---|
| Recipient output | 30,000 sats |
| Change output | 69,000 sats |
| Transaction fee | 1,000 sats |
| Total consumed | 100,000 sats |
The input is fully consumed. Two new outputs are created. The fee is the difference: 100,000 − 30,000 − 69,000 = 1,000. These are example amounts, not a recommended fee. Inputs, outputs, and fees.
Change is an output, too
Wallet software can send change to a new address it controls. That does not mean funds were lost or paid to a stranger. The wallet must track the relevant keys and outputs to calculate the balance correctly. Wallet behavior.
Why many small outputs matter
Using additional inputs generally increases transaction size. When miners prioritize fees relative to transaction weight, assembling many small outputs can cost more than spending one larger output of the same total value. The bitcoin amount alone does not determine the fee. Transaction structure.
Where the cash analogy stops
A UTXO is not a banknote with a fixed denomination. Transactions can create outputs of many amounts, and spending can depend on conditions more complicated than one signature. The analogy is useful for understanding whole-input consumption and change, but the actual rule is implemented through transaction scripts. Spending conditions.
Continue to mining and proof of work to see how transactions enter blocks.