Bitcoin has no account balances. Your balance is the total of unspent transaction outputs (UTXOs) your keys can unlock. Learn how UTXOs work.
No accounts, just outputs
A bank keeps one number per account. Bitcoin doesn't. It keeps a list of every unspent transaction output (UTXO): pieces of bitcoin that have been created but not yet spent.
Your wallet's balance is simply: add up every UTXO your keys can unlock.
Spending a UTXO
- A UTXO is always spent in full. Need 0.3 BTC but only have a 0.4 BTC UTXO? Spend all 0.4, send 0.3 to the payee and about 0.1 back to yourself as change.
- Once spent, a UTXO is gone forever and new UTXOs exist instead.
- Each node keeps the current set of all UTXOs (the UTXO set) so it can check new transactions quickly.
Why this design?
- Easy to verify: a node only needs to check that each input points to a UTXO that exists and is unspent.
- Prevents double spending: once a UTXO is spent, any other transaction spending it is invalid. See The double-spending problem.
- Parallel: unrelated UTXOs can be checked independently.
UTXOs vs accounts
| UTXO model (Bitcoin) | Account model (banks) | |
|---|---|---|
| What's stored | A list of unspent coins | One balance per account |
| Spending | Consume whole coins, make change | Subtract from the balance |
| Parallel checking | Easy: coins are independent | Harder: balances change in order |
| Privacy | New addresses per coin help | One account links everything |
How big is the UTXO set?
Every full node keeps the set of all unspent outputs, tens of millions of entries, in a fast database. That set is what a node checks to decide whether a new transaction's inputs are real. It's also why tiny unspendable outputs are discouraged: every one of them costs every node memory. See Dust and UTXO consolidation.
Key takeaways
- Bitcoin tracks unspent outputs, not account balances.
- A UTXO must be spent in full; extra value returns as change.
- Your balance is the total of the UTXOs your keys can spend.
Common questions
How many UTXOs does a wallet have?
As many as payments it has received and not yet spent, plus change outputs. Active wallets often hold dozens.
Is having many small UTXOs bad?
It makes future transactions bigger and more expensive. See consolidation.
What does UTXO stand for?
Unspent transaction output: an output that has been created and not yet spent.
How do I see my UTXOs?
Most desktop wallets have a 'coins' or 'UTXOs' tab. You can also look up each address on MyBitcoinExplorer.