UTXOUTXO
An unspent transaction output (UTXO) is a piece of cryptocurrency received in an earlier transaction and not yet spent. Bitcoin tracks balances as collections of UTXOs, unlike Ethereum, which keeps account balances.
A UTXO, or unspent transaction output, is a chunk of bitcoin that has been received and not yet spent. A Bitcoin wallet balance is really the sum of these chunks. Understanding UTXOs explains change outputs, why some transactions cost more in fees, and how Bitcoin differs from account-based chains like Ethereum.
- Category
- Cryptocurrency and Blockchain
- Reading time
- 4 min
- Also called
- Unspent transaction output, UTXO model, Coin outputs
- Updated
UTXO in plain words
A UTXO — unspent transaction output — is a chunk of bitcoin that can be used as an input in a new transaction.1
Instead of one account balance, the UTXO model records separate amounts, each created by an earlier transaction.2
Think of them as banknotes of odd sizes: you spend whole notes and get change back.
How a UTXO transaction works
Pick inputs
Your wallet selects UTXOs that add up to at least the amount you want to send.
Only unspent outputs
Only unspent outputs can be used as inputs; otherwise the payment is invalid.3
Create outputs
One output pays the recipient.
Send change back
Often a further output returns “change” to the sender.2
Leave a fee
Whatever input value isn't assigned to outputs can be collected by the miner as the fee.3
Outputs become new UTXOs
Once confirmed, the spent inputs are gone and the new outputs can be spent later.
Worked examples
Example 1 — Paying with change
0.2999 BTC returned as changeA hypothetical wallet holds one 0.5 BTC UTXO and pays 0.2 BTC with a 0.0001 BTC fee.
| Payment | 0.2 BTC |
| Change | 0.5 − 0.2 − 0.0001 = 0.2999 BTC |
This is the typical shape: one output pays the recipient and another sends change back.4
Example 2 — Forgetting change
0.7 BTC lost to feesA hypothetical user builds a transaction by hand using a 1.0 BTC UTXO to pay 0.3 BTC and adds no change output.
| Inputs minus outputs | 1.0 − 0.3 = 0.7 BTC |
| Paid as fee | 0.7 BTC |
The miner keeps the difference — any input value left over after the outputs becomes the fee.3
Example 3 — Many small inputs
12,240 sats more in feesA hypothetical wallet pays using 10 small UTXOs instead of 1 large one, with each input adding about 68 vbytes at 20 sat/vbyte.
| Extra inputs | 10 − 1 = 9 |
| Extra size | 9 × 68 = 612 vbytes |
| Extra fee | 612 × 20 = 12,240 sats |
Every output on the chain is either unspent or already spent, and only unspent ones can be inputs.3
UTXO model vs account model
| Aspect | UTXO (Bitcoin) | Account (Ethereum) |
|---|---|---|
| How balance is stored | Sum of unspent outputs | A single balance per address |
| Change | Returned as a new output | Not needed |
| Fee drivers | Number of inputs and outputs | Computation used (gas) |
| Privacy | Can use fresh addresses per output | Address reuse is common |
Why traders should know UTXOs
Fee planning
Consolidate small UTXOs when Trading Fees and Commissions on-chain are low.
Exchange deposits
Understand how Settlement of deposits works on-chain.
On-chain analysis
UTXO age data feeds Fundamental Analysis.
Profit tracking
Each UTXO has its own cost basis for Realized and Unrealized P&L.
Advantages and disadvantages
Advantages
- Each coin's history is easy to verify.
- Supports parallel checking of transactions.
- Change addresses can improve privacy.
- Double spends are simple to detect.
Disadvantages
- Many small UTXOs raise fees.
- Change outputs confuse new users.
- Harder to build complex smart contracts.
- Manual mistakes can send change as fees.
Going deeper
Read as far as you need. Each level builds on the one before it.
Balance is a sum
Beginner
A wallet balance is just the sum of all the unspent outputs it can spend.1
Combining and splitting value
Intermediate
Most payments have one or two outputs: the payment itself and, if needed, change back to the sender.4 Wallets choose which inputs to combine, which affects fees and privacy.
UTXO vs account ledgers
Advanced
The Fed notes that unlike Bitcoin, Ethereum records information via account addresses.2 The UTXO design makes validation simple but pushes coin selection and change handling onto wallets.
Common mistakes
Forgetting the change output
Leftover value becomes a fee.
Ignoring dust
Tiny UTXOs can cost more to spend than they hold.
Consolidating at peak fees
Merge UTXOs when the network is quiet.
Assuming one balance
Wallets track many separate outputs.
Check your understanding
Test yourself before moving on. Each answer comes with an explanation.
Key points to remember
- A UTXO is an output not yet spent.
- Bitcoin balances are sums of UTXOs.
- Payments usually create a change output.
- Inputs minus outputs equals the fee.
- Many small inputs raise fees.
Frequently asked questions
Does Ethereum use UTXOs?
What is UTXO consolidation?
Why did my wallet send coins to a new address?
Further learning
- Settlement
How on-chain transfers settle.
- Trading Fees and Commissions
What drives transaction costs.
- Realized and Unrealized P&L
Tracking gains per coin lot.
- Fundamental Analysis
Reading on-chain data.
Sources
This article is written in our own words. The sources below support the specific facts, rules and figures marked with a number in the text. Links open the original publisher’s page.
- Bitcoin Project (developer.bitcoin.org). Glossary (opens in a new tab) Checked .
- Board of Governors of the Federal Reserve System. Tokens and accounts in the context of digital currencies (FEDS Notes) (opens in a new tab) Checked .
- Bitcoin Developers (bitcoindevelopers.org). Block Chain developer guide (opens in a new tab) Checked .
- Satoshi Nakamoto. Bitcoin: A Peer-to-Peer Electronic Cash System (opens in a new tab) Checked .
Educational content, not financial advice. Examples use hypothetical prices and simplified costs; actual fees, margin rules and regulations vary by broker, market and country. We are not affiliated with any publisher linked above. Last reviewed . Report an error or request a source credit.