What Bitcoin Change Outputs Mean When You Make a Swap
A Bitcoin change output returns unused input value to your wallet after a swap deposit; knowing where it goes helps you read the transaction correctly.
BitCurrent Newsroom2 min read
A Bitcoin change output sends the unused part of a transaction’s inputs back to your wallet when you fund a swap. It is a normal Bitcoin output, separate from the amount sent to the swap destination.
- Input: 0.0100 BTC
- Swap deposit: 0.0060 BTC
- Network fee: 0.0001 BTC
- Change returned: 0.0039 BTC
These figures are an example: the wallet selects one or more spendable outputs, then builds the transaction around the requested deposit and fee. For the route choices behind a Thor swap, read how Thor swap routes differ. That helps explain the swap path; change is about how the Bitcoin transaction is funded.
Why does a Bitcoin transaction create change?
Bitcoin spends whole unspent transaction outputs, or UTXOs. A wallet cannot spend only part of one UTXO, so it creates outputs that account for the value it uses.
If an input is worth more than the deposit plus the fee, the wallet usually creates a second output back to an address it controls. That output becomes a new UTXO the wallet can spend later.
Is change part of the swap?
No. The swap deposit is the amount sent to the destination specified by the swap flow. Change stays under your wallet’s control and is not included in that deposit.
The wallet calculates the fee separately. In the example, 0.0100 BTC in equals 0.0060 BTC to the swap destination, 0.0039 BTC in change, and 0.0001 BTC in fees. Actual amounts depend on the selected inputs, the requested deposit, and the fee chosen.
How can you identify the change output?
Your wallet can identify its own change because it knows which output scripts it controls. A public transaction record shows outputs and amounts, but it does not label one as “change”; outside observers may only infer that from transaction patterns.
Check the destination and amount shown in the wallet before signing. If the transaction has a change output, verify that it returns to an address your wallet recognizes. The useful distinction is simple: the swap output leaves your wallet for the swap, while change remains yours.