Bitcoin does not track balances the way a bank account does. Instead it tracks individual pieces of received coin, each called an unspent transaction output. Your wallet balance is really just the sum of all the UTXOs your keys control. When you spend, you consume whole UTXOs as inputs and the transaction creates new ones as outputs, one to the recipient and, if needed, one of change back to yourself.
A familiar analogy is cash. If you pay for a six-pound item with a ten-pound note, you hand over the whole note and receive four pounds in change. UTXOs work the same way: you cannot spend part of one, so you consume it entirely and get change back as a fresh UTXO. This is why a wallet's history is full of small change outputs.
The model has real advantages in transparency and parallel verification, and it is central to how Bitcoin and similar chains work under the hood. Ethereum, by contrast, uses a simpler account-balance model. For everyday users the UTXO machinery is invisible, but it explains quirks like why fees can depend on how many small pieces make up your balance. Some wallets even let you inspect and choose among your individual UTXOs, a practice called coin control that more advanced users rely on to manage fees and privacy.
Key takeaways
- A UTXO is an unspent piece of received cryptocurrency that serves as an input to future transactions.
- Your balance is the total of all UTXOs your keys control, not a single stored number.
- Spending consumes whole UTXOs and produces new ones, including change, much like paying with cash and receiving change.
UTXO — часто задаваемые вопросы
Do all blockchains use UTXOs?
No. Bitcoin and several others use the UTXO model, while Ethereum and many newer chains use a simpler account-balance model that tracks a running total for each address rather than individual coin pieces.
Why does my wallet have so many small transactions?
Those are usually change outputs. Because you must spend whole UTXOs, most payments send some coin back to yourself as change, which accumulates as many small unspent pieces over time.
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