UXTO Management: How Do I Consolidate UTXOs?

In the Bitcoin protocol, Unspent Transaction Outputs (UTXOs) are used as an accounting model to define the beginning and end of a transaction. The UTXO model allows you to manage your digital currency balances without a central authority, giving you complete control over your funds.

In this guide, you will learn what UTXOs are and how they work, and discover UTXO management best practices you should employ. 

What Are Unspent Transaction Outputs? 

Unspent Transaction Output (UTXO) is the amount of unused bitcoin (BTC) you have after executing a transaction. 

All Bitcoin transactions have an input (UTXO to be consumed) and output (generated UTXO). When a transaction is executed, the input is consumed, and an output is generated. A transaction's output can be spent (used in the transaction) or unspent. 

UTXO is the unspent output after a transaction representing the digital currency left over after a transaction that can be spent as input in the next transaction. In other words, your UXTOs are the BTC you have in your wallet right now. 

How Do Bitcoin Transactions Work? The UTXO Model Explained 

The Bitcoin blockchain is a peer-to-peer (P2P) distributed network that stores transaction data on a public ledger. It consists of a chain of blocks cryptographically linked together to form an immutable ledger. 

The blockchain is distributed across multiple systems called nodes that store and maintain updated copies of the network’s data, including transaction data, previous blocks hash, timestamps, and other metadata. 

Bitcoin is based on the UTXO blockchain model to keep track of transactions.

How Does the UTXO Model Work?

The UTXO model is the fundamental building block of Bitcoin transactions. Every Bitcoin transaction is made of an input and output. 

Different structures build a transaction, including:

• Transaction version number
• Input
• Output
• Locktime

When you execute a Bitcoin transaction, you take one or more UTXOs (funds available from previous transactions) and spend them as input. 

The transaction structure starts with a version number that specifies the transaction type you are making, helping the node determine what rules apply in verifying the transaction.

Every transaction input has a pointer that points back to a specific UTXO and an unlocking key that unlocks the corresponding output. The key is usually the sender's signature, which proves bitcoin ownership. The transaction output has a cryptographic lock that can be unlocked by the input key and value that shows the amount of bitcoin locked in the output. 

Lastly, the transaction structure has Locktime, which defines when a transaction is valid and can be added to the blockchain immediately or after some time. When an input unlocks an output, the blockchain network marks it as ‘spent,’ and it is removed from the circulating supply. That indicates the transaction is completed, and the unspent output becomes the new UTXO. 

Unspent transaction outputs are outputs from a transaction that haven't been unlocked as inputs. Every UTXO is an indivisible chunk of bitcoin denominated as in satoshis, the smallest unit of bitcoin, with a fixed value and a unique identifier. 

The Bitcoin blockchain recognizes UTXOs as currency units and tracks all unspent outputs without accounts and balances, like other accounting models.

The network nodes have a local copy of UTXOs available, which allows the nodes to verify transactions efficiently. The compilation of all UTXOs is also maintained by nodes and is updated every time a new block is added to the blockchain. Only unspent outputs can be used for new transactions, preventing currency double-spending. 

UTXOs are indivisible once created, meaning if the required transaction is a fraction of the available UTXOs, the whole UTXO must be consumed in the transaction, and the change will be generated as a new UTXO.

For instance, if you have a 10 BTC UTXO and want to send 4 BTC to a friend, your transaction must consume the entire 10 BTC UTXO and produce two outputs: one output is sending the 4 BTC to your friend, and the other is giving back a UTXO worth 6 BTC to your wallet as “change.”

Therefore, most Bitcoin transactions generate change, and users end up with several UTXOs of various units. Your Bitcoin wallet can automatically track and manage your UTXOs to give you your final balance.

What Are the Advantages of the UTXO Model?

• Enhanced privacy and security: The UTXO model contributes to user security and privacy since it ensures every transaction only spends specified UTXOs without revealing your entire balance, and they don't link to identities directly. Transactions cannot be executed without user verification.
• Prevents double-spending: Since only unspent outputs can be used for new transactions, transaction authentication is easier, which prevents double-spending.
• Provides a clear audit trail: The model has a clear transaction history, which makes it easy to track the movement of digital currency in the network.
• Improves transaction verification efficiency: The model makes it easier for nodes to verify transactions since each UTXO is independent. Users can process multiple UTXOs at once, potentially speeding up the verification process and improving scalability.
• Supports decentralized exchanges: The UTXO model allows P2P exchange without central authority intervention.

What Are the Weaknesses of the UTXO Model?

• Lack of programmability and smart contract support.
• Many inputs can lead to high transaction fees and require more storage and processing power.
• The model is less intuitive than other accounting models.

What Is UTXO Consolidation?

UTXO consolidation is the process of reducing the number of small UTXOs by turning them into a single bigger UTXO. 

Since every transaction has a unique UTXO, you can quickly grow a long list of UTXOs. Consolidation helps you streamline the management of your funds. It's like going to the bank to change a bunch of coins for a big bill. 

There are two main types of UTXO consolidation;

• Manual consolidation: This technique involves manually creating a new transaction, carefully selecting your desired UTXOs as input, and sending them to your address as a new output. This method gives you more control over your funds but requires active management of UTXOs.
• Automatic consolidation: This technique is a hands-off approach that uses your wallet to merge multiple UTXOs automatically. Your Bitcoin wallet takes charge of your UTXOs based on specific conditions you set autonomously. The wallet will generate new transactions by selecting multiple UTXOs and consolidating them into a single output at regular intervals. 

Manual consolidation gives you greater control and visibility over your UTXOs, while automatic consolidation makes UTXO management easier.

Why Is UTXO Consolidation Important?

Frequently running operations on Bitcoin and buying BTC can leave you with many UTXOs, which can be challenging to manage over time. Additionally, when crafting a transaction, the number of UTXOs affects how much fees you pay for the transaction. Bitcoin network fees can become hefty at certain times, which poses a problem for users with many UTXOs.

Your transaction size is determined by the number of UTXOs you use as input. The more UTXOs there are, the larger your transaction and the more miners will charge you in fees.

Therefore, consolidating your UTXOs reduces your input count for future transactions and potentially minimizes the fees you have to pay. It also streamlines UTXO management and helps reduce the Bitcoin network's UTXO set, making it easier to run nodes.

How Does UTXO Consolidation Save Fees?

UTXO consolidation reduces the number of inputs in transactions. 

Bitcoin transactions work similarly to cash transactions, where multiple UTXO inputs act like cash in different denominations. Imagine paying for a $100 tab with quarters. The vendor will have a hard time counting all the coins compared to when you pay using a single $100 note. 

That is the same case with UTXO inputs and miners on the Bitcoin network. 

The more UTXOs you use as input, the larger the transaction size and the bigger the burden on miners. Therefore, miners will charge you more to process large transactions with multiple UTXO inputs. The fee is calculated by multiplying the transaction size with the chosen rate.

Consolidating UTXOs can reduce future transaction fees by combining multiple small UTXOs into a single large output. Fewer inputs mean less data for the network to process, which saves on future costs.

UTXO Management Best Practices

UTXOs are a building block for Bitcoin’s architecture. However, the accumulation of UTXOs can be a hindrance and have implications for cost and security. UTXO management is an efficient way to streamline Bitcoin payments. 

Here are some of the best practices for UTXO management: 

• UTXO consolidation: This technique ensures you use fewer UTXOs, which lowers transaction fees and speeds up confirmation time. Although sending UTXO back to yourself for consolidation also incurs fees, it can be more efficient to save future fees if timed right.
• Strategic timing: Executing transactions, and especially consolidation, when the network is less congested, can significantly reduce the transaction fees. 
• Use fee estimation tools: Choose a few estimation tools to help you determine the optimal transaction fee. Striking the ideal balance helps ensure you don’t unnecessarily pay inflated costs by overpaying or have to wait for long confirmation times for underpaying. 
• Use multiple addresses: Using different addresses helps distribute your total balance in each transaction, thus enhancing privacy and security. 

To securely manage all your Bitcoin assets in one place, download Xverse today. 

How do I consolidate my UTXOs in Xverse?

Currently, the best way to consolidate your UTXO set in Xverse is to create a transaction from the desired address that includes those small UTXOs and send it to yourself (back to the address). This is usually accomplished by sending the entire balance consolidating all your UTXOs into one UTXO. The smaller the transaction you send to yourself, the less consolidated your UTXOs will be.

The default BTC API used in Xverse is https://mempool.space/api/, which sets a limit of 500 UTXOs per address. If your address has reached the UTXO limit set by mempool.space, you may receive an Axios 400 error message when trying to send Bitcoin.

Users can fix this issue by going to Settings > Change Network > Edit the BTC API URL to be  https://btc-1.xverse.app > Save.

You should now be able to consolidate your UTXOs and transact normally.

Frequently Asked Questions

Is Bitcoin a UTXO?

Bitcoin is a distributed ledger network that uses UTXO as part of its database technology. UTXO stands for Unspent Transaction Output and is a way to track funds on the Bitcoin network and prevent double-spending. UTXO represents bitcoin left over after you execute a transaction on the network. It's an accounting model that plays a critical role in how transactions are processed and the security of the blockchain.

How are UTXOs created?

UTXOs are unspent outputs, that is, the amount of bitcoin you have left after a transaction is completed. Every transaction on the Bitcoin network has inputs and outputs. When you make a transaction, the UTXOs are used as input to unlock the output. The UTXO is consumed as input to generate a new UTXO as output. When a transaction is completed, the unspent output gets sent back to your wallet as the new UTXO.

How does UTXO prevent double spending?

In the UTXO model, Bitcoin uses nodes to keep track of UTXOs and note which coins have been used and who can spend the unspent coins. UTXO transactions link inputs and outputs in a way that allows nodes to have an easier time authenticating and verifying whether the UTXOs being spent are valid. The model can prevent double-spending without needing third parties because only unspent outputs can be used as inputs to initiate a transaction.

Who invented UTXO?

While the conceptual framework of UTXO can be traced back to Hal Finney and his ‘Reusable Proof Of Work (RPOW)’ publication, its first widespread use was implemented by Bitcoin creator Satoshi Nakamoto when they launched Bitcoin in 2009. The original Bitcoin script relies heavily on the model, and all forks of the Bitcoin network use UTXO.

Which blockchain uses UTXO?

Bitcoin, the largest blockchain that uses the UTXO model, uses the accounting model to foster transparency and streamline transaction management. Other notable blockchains that use UTXO include Litecoin, Dogecoin, and Bitcoin forks like Bitcoin Cash. Some newer networks, like Cardano, use an extended version of the model.

What is a UTXO address?

UTXO are individual chunks of bitcoin that exist on an address. Bitcoin wallets can generate numerous unique addresses where you can store your UTXO. The network keeps track of your UTXO addresses and the value of the UTXO. The same addresses can have an infinite number of unspent outputs.

What is an example of a UTXO?

Unspent Transaction Output (UTXO) is the amount of cryptocurrency left behind after a transaction. An example is when you have UTXO worth 3 BTC in your Bitcoin Ordinals wallet and want to use 2 BTC for a purchase. When you execute the transaction, the whole 3 BTC UTXO will be consumed, and two outputs will be generated: one to send the 2BTC and another to return the 1 BTC UTXO change to your wallet.

UTXO model vs. accounts model: What’s the difference?

UTXO and accounts models are accounting techniques used in different blockchain networks to manage transactions. The most significant difference between the two models is with bookkeeping, where UTXO doesn’t keep the balance of the users, but accounts keep track of balances in user accounts. UTXO doesn't create an account for you or keep a record of your balance on the ledger, whereas accounts work like bank accounts where credit is added to the user's balance and debit is deducted directly.