The UTXO model is the foundation of Bitcoin and many other cryptocurrencies. It is precisely because of this model that bitcoins are often compared to cash. To understand why, it is important to see how coins are actually “stored” and transferred within the network.
UTXO stands for Unspent Transaction Output — an output of a transaction that has not yet been spent. Simply put, it is cryptocurrency that has been received but not yet used. When someone sends you bitcoins, you do not just see a higher balance. In the blockchain, a new UTXO is created—a separate record. If you receive funds multiple times, you will have several such “coin-records.” Their total is what appears as your wallet balance.
Each UTXO contains information about the number of coins, the recipient’s address, the unique transaction identifier (TxID), and the mechanism confirming ownership via a digital signature.
This model was first implemented in Bitcoin and later adopted by other projects such as Litecoin, Dogecoin, Bitcoin Cash, and Zcash. In the latter case, shielded UTXOs are used, allowing transaction details about the sender and recipient to be hidden. The Cardano platform applies an extended version of this model called EUTXO, which is adapted for smart contracts.
To better understand how UTXO works, it helps to compare it with cash. Imagine you received two banknotes: one worth 3 BTC and another worth 2 BTC. Although your wallet shows a total balance of 5 BTC, technically these are two separate “coins.” If you want to send someone 4 BTC, you would need to use both. They are spent entirely, and new outputs are created: 1 BTC to the recipient and 1 BTC as “change,” which returns to you at a new address. The old UTXOs disappear, and new ones appear instead. That is why people say there is no traditional account balance update in Bitcoin — only the destruction of old outputs and the creation of new ones.
This approach differs from the model used in the banking sector and in blockchains such as Ethereum, BNB Chain, and Solana. In those systems, each address has a single balance. When funds are transferred, the sender’s balance decreases, and the recipient’s balance increases. In the UTXO model, the system works with separate “digital banknotes,” not with a single balance entry.
The UTXO model has significant advantages, one of the most important being protection against double-spending. In a traditional digital environment, data can be copied, so theoretically the same file or record could be “spent” twice. In Bitcoin, this is prevented by the UTXO model. Each unspent output is a separate unit and can be used only once. As soon as it is included in a new transaction, the network marks it as spent. From that moment on, it becomes invalid and cannot be reused. All nodes in the network verify this rule, so any attempt to spend the same coins twice is rejected.
Another important advantage is transparency. All transactions are recorded on the blockchain and publicly verifiable. This means that anyone can open a blockchain explorer such as Blockchair or OKLink, enter a wallet address, and see its transaction history. It is possible to check how much was received, what amounts were sent, and which UTXOs remain unspent. Addresses do not contain the owner’s name, but all financial activity within the network remains open and verifiable.
Such transparency increases trust in the system: every participant can independently confirm that the rules apply equally to everyone and that coins truly exist and are not created “out of thin air.”
However, the UTXO model also has disadvantages. One of them is the accumulation of so-called “dust.” Dust refers to very small amounts of bitcoin (usually a few hundred or thousand satoshis) that technically belong to the user but are impractical to spend. The reason is simple: the transaction fee may exceed the value of the UTXO. As a result, these tiny outputs remain in the wallet and may accumulate over time.
There is also a “dust attack.” In this case, attackers deliberately send tiny amounts to many addresses. By themselves, these transactions do not steal anything or grant access to funds. However, if a user later spends this “dust” together with other UTXOs in a single transaction, blockchain analysts may link different addresses and track the movement of funds. Thus, the main goal of dust attacks is not theft but a reduction of user privacy.
Another disadvantage of the UTXO model concerns data storage. All created transactions and all UTXOs are recorded on the blockchain and remain there permanently. They cannot be deleted or “cleaned up,” because the security of the network and the ability to verify the origin of every coin are built on this history.
As people continue to send and receive bitcoins, the volume of data grows. Each new block adds information about new transactions, thereby increasing the total database size. To run a full node and independently verify all operations, a user must download and store the entire copy of the blockchain. Over time, this requires more disk space and more powerful hardware.
Thus, the longer the network exists and the more actively it is used, the higher the technical requirements become for participants who want to support it at a full level.
Finally, an important feature of the UTXO model concerns how transaction fees are formed. When a user sends bitcoins, they use one or several of their UTXOs as transaction inputs. The owner’s digital signature must confirm each input individually. This proves that the sender has the right to spend those coins.
The more UTXOs are used in a single operation, the more data the transaction contains. In the Bitcoin network, the fee depends not on the amount being transferred but on the transaction size in bytes. Therefore, if a user has accumulated many small bitcoin amounts (e.g., 0.001 BTC each) and wants to send a larger amount, the system must combine these UTXOs into a single transaction. As a result, the transaction becomes larger, and the fee increases accordingly.
In other words, having many small outputs makes transactions more “heavy” from a technical perspective and can lead to higher transaction costs.
UTXO stands for Unspent Transaction Output — an output of a transaction that has not yet been spent. Simply put, it is cryptocurrency that has been received but not yet used. When someone sends you bitcoins, you do not just see a higher balance. In the blockchain, a new UTXO is created—a separate record. If you receive funds multiple times, you will have several such “coin-records.” Their total is what appears as your wallet balance.
Each UTXO contains information about the number of coins, the recipient’s address, the unique transaction identifier (TxID), and the mechanism confirming ownership via a digital signature.
This model was first implemented in Bitcoin and later adopted by other projects such as Litecoin, Dogecoin, Bitcoin Cash, and Zcash. In the latter case, shielded UTXOs are used, allowing transaction details about the sender and recipient to be hidden. The Cardano platform applies an extended version of this model called EUTXO, which is adapted for smart contracts.
To better understand how UTXO works, it helps to compare it with cash. Imagine you received two banknotes: one worth 3 BTC and another worth 2 BTC. Although your wallet shows a total balance of 5 BTC, technically these are two separate “coins.” If you want to send someone 4 BTC, you would need to use both. They are spent entirely, and new outputs are created: 1 BTC to the recipient and 1 BTC as “change,” which returns to you at a new address. The old UTXOs disappear, and new ones appear instead. That is why people say there is no traditional account balance update in Bitcoin — only the destruction of old outputs and the creation of new ones.
This approach differs from the model used in the banking sector and in blockchains such as Ethereum, BNB Chain, and Solana. In those systems, each address has a single balance. When funds are transferred, the sender’s balance decreases, and the recipient’s balance increases. In the UTXO model, the system works with separate “digital banknotes,” not with a single balance entry.
The UTXO model has significant advantages, one of the most important being protection against double-spending. In a traditional digital environment, data can be copied, so theoretically the same file or record could be “spent” twice. In Bitcoin, this is prevented by the UTXO model. Each unspent output is a separate unit and can be used only once. As soon as it is included in a new transaction, the network marks it as spent. From that moment on, it becomes invalid and cannot be reused. All nodes in the network verify this rule, so any attempt to spend the same coins twice is rejected.
Another important advantage is transparency. All transactions are recorded on the blockchain and publicly verifiable. This means that anyone can open a blockchain explorer such as Blockchair or OKLink, enter a wallet address, and see its transaction history. It is possible to check how much was received, what amounts were sent, and which UTXOs remain unspent. Addresses do not contain the owner’s name, but all financial activity within the network remains open and verifiable.
Such transparency increases trust in the system: every participant can independently confirm that the rules apply equally to everyone and that coins truly exist and are not created “out of thin air.”
However, the UTXO model also has disadvantages. One of them is the accumulation of so-called “dust.” Dust refers to very small amounts of bitcoin (usually a few hundred or thousand satoshis) that technically belong to the user but are impractical to spend. The reason is simple: the transaction fee may exceed the value of the UTXO. As a result, these tiny outputs remain in the wallet and may accumulate over time.
There is also a “dust attack.” In this case, attackers deliberately send tiny amounts to many addresses. By themselves, these transactions do not steal anything or grant access to funds. However, if a user later spends this “dust” together with other UTXOs in a single transaction, blockchain analysts may link different addresses and track the movement of funds. Thus, the main goal of dust attacks is not theft but a reduction of user privacy.
Another disadvantage of the UTXO model concerns data storage. All created transactions and all UTXOs are recorded on the blockchain and remain there permanently. They cannot be deleted or “cleaned up,” because the security of the network and the ability to verify the origin of every coin are built on this history.
As people continue to send and receive bitcoins, the volume of data grows. Each new block adds information about new transactions, thereby increasing the total database size. To run a full node and independently verify all operations, a user must download and store the entire copy of the blockchain. Over time, this requires more disk space and more powerful hardware.
Thus, the longer the network exists and the more actively it is used, the higher the technical requirements become for participants who want to support it at a full level.
Finally, an important feature of the UTXO model concerns how transaction fees are formed. When a user sends bitcoins, they use one or several of their UTXOs as transaction inputs. The owner’s digital signature must confirm each input individually. This proves that the sender has the right to spend those coins.
The more UTXOs are used in a single operation, the more data the transaction contains. In the Bitcoin network, the fee depends not on the amount being transferred but on the transaction size in bytes. Therefore, if a user has accumulated many small bitcoin amounts (e.g., 0.001 BTC each) and wants to send a larger amount, the system must combine these UTXOs into a single transaction. As a result, the transaction becomes larger, and the fee increases accordingly.
In other words, having many small outputs makes transactions more “heavy” from a technical perspective and can lead to higher transaction costs.