Wide Web Crypto / Knowledge library · Bitcoin · 2 min read
Start with spendable outputs
A Bitcoin wallet displays a total, but its money is organized into unspent transaction outputs, or UTXOs. Spending consumes particular outputs and creates new ones. Ask which receipts fund a payment, rather than imagine the network subtracting a number from one central account.
An output has an amount and spending conditions. The wallet finds outputs it can spend, prepares a transaction, and obtains signatures. The coins do not sit inside your device: the device supplies authorization for a change to public transaction history.
Follow a hypothetical payment
Suppose a wallet controls outputs of 70,000 and 50,000 satoshis. It needs to pay a recipient 90,000 satoshis and chooses both inputs. If the fee is 1,000 satoshis, the transaction creates a 90,000-satoshi recipient output and a 29,000-satoshi change output. Input value equals recipient value, change, and fee.
The original outputs cannot be partly retained after spending. Remaining economic value appears in the new change output. This explains why an explorer may show two destinations even when you intended one payment. Identifying a recipient solely by the larger output is an unreliable investigative shortcut.
| Component | Example amount | Purpose |
|---|---|---|
| Inputs | 120,000 sats | Previously spendable outputs |
| Recipient | 90,000 sats | Requested payment |
| Change | 29,000 sats | Value returned to sender |
| Fee | 1,000 sats | Input minus output value |
Coin selection affects cost and privacy
A wallet receiving hundreds of small payments may need many inputs for a later withdrawal. More inputs usually increase transaction size and therefore the fee at a given rate. A displayed balance alone cannot tell you what a future payment costs.
Combining outputs creates public clues that they may share an owner. That inference has exceptions, but matters when mixing personal, business, and donation receipts. Consolidation can simplify future spending while publishing relationships between outputs. The decision depends on fee conditions and your separation requirements.
An accounting record should distinguish incoming receipts from movements between your own addresses. Otherwise, consolidation can be mistaken for new revenue or a large outside payment. Preserve wallet labels locally; outsiders cannot reliably reconstruct intent from amounts alone. When reviewing a payment later, the label and invoice can be more informative than a visually prominent arrow in an explorer.
Before sending
- Compare the recipient amount, fee, and change shown by the wallet.
- Check whether selected outputs come from activities you intended to keep separate.
- Leave enough spendable value for fees; your total is not always the practical payment maximum.
- Record the transaction identifier and your own purpose label after broadcasting.
Frequently asked questions
Does a new receiving address create a new wallet?
No. A wallet can manage many receiving and change addresses. Its balance can include outputs associated with all of them.
Does unspent mean unconfirmed?
No. Unspent describes whether an output has been consumed. Confirmation describes inclusion in the accepted chain. These properties answer different questions.