A friend asked me about this privately, so here's a plain-English explanation.

Bitcoin and Ethereum both keep track of “who has how many coins,” but they do it in completely different ways: Bitcoin records individual “unspent bills,” while Ethereum records each account’s balance. Once you understand the difference, a lot of things that seem strange start to make sense.

Coin mentioned in the article: $BTC trading at 81,039.09 (24h -0.23%).

【UTXO: Unspent Bills】

Bitcoin uses the UTXO (Unspent Transaction Output) model. You can think of each UTXO as a bill of varying denomination: each transaction spends some old bills and creates some new ones for the recipients.

The balance shown in your wallet is calculated by adding up all the UTXOs that belong to you. There is no number called a “balance” on the blockchain.

【Change and transaction fees】

A UTXO can only be spent in its entirety. For example, if you have a “bill” worth 1 coin and need to pay 0.3 coins, the transaction creates two outputs: 0.3 coins go to the other person, and the remainder, minus the transaction fee, is returned to one of your own addresses as change. Many wallets send change to a new address, so in a block explorer you may see that “the money was sent back to yourself.”

Bitcoin transaction fees aren’t listed separately. Instead, they equal the sum of all inputs minus the sum of all outputs, and the miner who includes the transaction in a block receives this difference.

【The account model: balances recorded directly】

Ethereum uses the account model, in which each account’s balance is recorded directly on the blockchain. A transfer deducts funds from one account and adds them to another, much like a bank account. Ethereum has two types of accounts: externally owned accounts controlled by private keys, and contract accounts controlled by code.

To prevent the same transaction from being executed twice, every externally owned account has a nonce, which increases by 1 with each transaction. Transactions must be executed in nonce order, so if an earlier transaction gets stuck, later transactions will have to wait in line too.

【Each has its trade-offs】

In the UTXO model, unrelated transactions can be verified in parallel, and using new addresses for change can also help protect privacy. However, writing complex contracts is less convenient. The account model makes balances easy to understand and contracts easier to write, but transactions from the same account must be processed in order. Cardano builds on UTXO with an extension called eUTXO, which allows outputs to carry script logic.

【Final thoughts】

Next time you see Bitcoin “sent back to yourself” in a block explorer, or an Ethereum transaction get stuck and cause all later transactions to queue up, you’ll know these are simply characteristics of two different accounting models—no need to panic. Every potential reward comes with its own risks, so understand the worst-case scenario first.

Have you run into any pitfalls related to this? Share your experience to help others stay alert.

This does not constitute a trading signal.