What is a UTXO?
The technical term for "pieces" of bitcoin that can be spent. Your wallet balance is the sum of all UTXOs you control.
Why It Matters
Understanding UTXOs demystifies how Bitcoin actually works behind the scenes. Bitcoin doesn't track account balances like traditional banking. Instead, it tracks UTXOs—unspent outputs from previous transactions. Your wallet balance is calculated by adding up all the UTXOs you control. When you send bitcoin, you select UTXOs to spend as inputs and create new UTXOs as outputs. This is why transaction history matters; to spend a UTXO, you need to prove you created it in a previous transaction and haven't spent it elsewhere. This design prevents double-spending and is elegant but different from traditional money concepts. More complex wallets show UTXO management, which helps optimize transaction fees.
How It Works
Bitcoin's ledger is structured as inputs and outputs, not account balances. When you receive bitcoin, a transaction creates a UTXO with your name on it. That UTXO can be spent once and only once. When you spend it, it becomes the input to a new transaction that creates new UTXOs. Your wallet's balance is the sum of all UTXOs you can unlock with your keys. Because each UTXO can only be spent once, Bitcoin prevents double-spending—you can't use the same UTXO in multiple transactions. When your wallet sends payment, it selects UTXOs totaling at least the sending amount, spends them, and creates output UTXOs to the recipient and yourself (change).