# UTXOs: how Bitcoin balances really work

Bitcoin has no account balances. Your balance is the total of unspent transaction outputs (UTXOs) your keys can unlock. Learn how UTXOs work.

Canonical page: https://mybitcoinexplorer.com/learn/understanding-utxos
Topic: Transactions
Published: 2026-10-29
Updated: 2026-10-30


## 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.

> Diagram: Spending consumes whole UTXOs and creates new ones — 0.4,0.25,0.1 → 0.7,0.0499

## 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](https://mybitcoinexplorer.com/learn/change-outputs).
- 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](https://mybitcoinexplorer.com/learn/double-spending-problem).
- **Parallel:** unrelated UTXOs can be checked independently.

> When analysts trace funds, they follow UTXOs from transaction to transaction. Which input "paid" which output is not recorded, so tracing always involves assumptions. See [What a Bitcoin trace can and can't prove](https://mybitcoinexplorer.com/learn/tracing-bitcoin).


## 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](https://mybitcoinexplorer.com/learn/dust-and-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.

## Related lessons

- [What is a Bitcoin transaction?](https://mybitcoinexplorer.com/learn/what-is-a-bitcoin-transaction)
- [Change outputs](https://mybitcoinexplorer.com/learn/change-outputs)
- [Dust and UTXO consolidation](https://mybitcoinexplorer.com/learn/dust-and-consolidation)
- [Coin control](https://mybitcoinexplorer.com/learn/coin-control)