Unspent Transaction Output (UTXO)

November 21, 2023 - Around 2 mins mins to read

Understanding Unspent Transaction Output (UTXO)

In the realm of cryptocurrency, an unspent transaction output (UTXO) refers to a blockchain transaction output that has not been used as an input in any subsequent transaction.

Bitcoin, the most well-known cryptocurrency, utilizes this model.

Each bitcoin transaction consists of an input and an output. The input indicates the address from which the bitcoin is sent, while the output represents the address to which it is sent.

The user possesses the output of a transaction and can spend it in a future transaction. This is different from bank accounts, which keep track of debits and credits and provide a statement with a running balance at the end of each month.

In the UTXO model, the total balance or wealth in a wallet is the sum of all unspent transaction outputs. It is similar to receiving change after making one or more purchases, which can be used for future transactions.

For example, let’s consider Bob, who has 10 coins and wants to send two coins to Alice. Bob’s wallet first unlocks the 10-coin UTXOs and uses all 10 coins as input for the transaction. This transaction sends two coins to Alice’s address, while the remaining eight coins are sent back to Bob as a new UTXO to a newly created address.

If Alice had three coins before the transaction, her wallet now keeps track of two UTXOs: one from before and the other from Bob’s transaction.

In the UTXO model, the total inputs must be equal to or greater than the total outputs. This is one of the initial checks validators perform to verify the validity of a transaction.

UTXO is particularly effective in decentralized systems as it can easily detect instances of double spending in a computationally efficient manner.

Glossary