KoinlyticsEthereum has accounts with balances. Bitcoin does not. Bitcoin has UTXOs: unspent transaction outputs, each a discrete chunk of value locked to some conditions. Your wallet balance is the sum of the UTXOs you can spend.
How a transaction actually looks
A transaction consumes one or more UTXOs as inputs and creates one or more new UTXOs as outputs. If your inputs sum to more than what you are sending, one output goes back to you as change. The miner keeps the leftover as the fee. You do not "transfer" from a balance. You destroy old UTXOs and mint new ones.
If you have a 1 BTC UTXO and want to send 0.3 BTC, the transaction has one input (1 BTC) and two outputs (0.3 to the recipient, 0.7 back to you). The 1 BTC UTXO is now spent forever.
Why this matters for fees
Fees in Bitcoin are per byte of transaction data, not per coin sent. A transaction with 20 inputs is much bigger and costs much more than one with a single input, even if the amounts are identical. Wallets that let dust UTXOs pile up eventually become expensive to spend. The single most useful wallet feature nobody uses is coin control.
The mempool
When you broadcast a transaction, it does not go straight into a block. It goes into every node's mempool, a memory buffer of unconfirmed transactions. Miners pick the most fee-per-byte-profitable transactions to include in the next block. If fees spike (BRC-20 inscriptions, ordinals mania), your low-fee transaction can sit in mempool for days or get evicted entirely.
RBF and CPFP
- Replace-By-Fee (BIP-125). If your transaction is stuck, broadcast a replacement with a higher fee and the same inputs. Miners will pick the more profitable one.
- Child-Pays-For-Parent. If a low-fee transaction sent you money, you can spend its output with a very high fee. Miners must include the parent to make the child valid, so both get confirmed.
Privacy implication
Every UTXO's history is fully public. Chain analysis firms group UTXOs into clusters using common-input heuristics: if two UTXOs are spent in the same transaction, they probably share an owner. This is why serious privacy on Bitcoin requires coinjoins or Lightning, not just "a new address for every payment."