Blockchain Deep Dive
Bitcoin Transactions and UTXOs
Cryptography, the UTXO model, chain types, scaling, and tokenomics.
In this lesson
- Bitcoin's UTXO accounting model
- How it differs from account balances
Key takeaways
- 1Your balance is the sum of unspent outputs (UTXOs)
- 2Each spend consumes UTXOs and creates new ones
- 3Ethereum instead tracks account balances directly
Lesson summary
Bitcoin tracks ownership through UTXOs, or unspent transaction outputs.
Mental model
Bitcoin Transactions and UTXOs in plain terms
Bitcoin tracks ownership through UTXOs, or unspent transaction outputs. Instead of one account balance changing, coins are represented as chunks that are consumed and recreated.
- Bitcoin's UTXO accounting model
- How it differs from account balances
Mechanics
How to reason about Bitcoin transactions and UTXOs
A transaction spends existing UTXOs and creates new UTXOs.
Wallet balance is the sum of spendable outputs controlled by the wallet.
Ethereum-style account models update account balances directly.
- Your balance is the sum of unspent outputs (UTXOs)
- Each spend consumes UTXOs and creates new ones
- Ethereum instead tracks account balances directly
Example
Bitcoin Transactions and UTXOs in practice
If you control one 1 BTC UTXO and send 0.3 BTC, the transaction can create 0.3 BTC for the recipient and about 0.7 BTC back to your change address, minus fees.
Common mistakes
The usual Bitcoin transactions and UTXOs trap
Users may think a Bitcoin wallet has one simple balance on-chain. Under the hood, wallet software selects UTXOs to fund each spend.
Risk notes
What can go wrong with Bitcoin transactions and UTXOs
Poor UTXO management can increase fees, reduce privacy, or create dust that is expensive to spend.
- Define UTXO.
- Explain change output.
- Compare UTXO with account balance models.
Practice
Make Bitcoin transactions and UTXOs stick
- Define UTXO.
- Explain change output.
- Compare UTXO with account balance models.
Review
Key terms
- Address
- A public identifier (a string of characters) where crypto can be sent on a blockchain. Safe to share — it does not expose your private key.
- Bitcoin (BTC)
- The first cryptocurrency, launched in 2009 — a decentralized, hard-capped (21M) digital money.
- Blockchain
- A shared, append-only ledger replicated across many computers, secured by cryptography and consensus.
- Ethereum (ETH)
- A programmable blockchain — a 'world computer' that runs smart contracts and dApps.
- Tokenomics
- The economic design of a token — its supply, demand, incentives, and distribution.
Source notes
Editorial references
These references are starting points for verifying the mechanisms, risk checks, and product context behind this lesson.
Before you continue
Can you do these?
- Define UTXO.
- Explain change output.
- Compare UTXO with account balance models.
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In Bitcoin's UTXO model, your balance is…