Change outputs and where a balance sits
Bitcoin cannot spend part of a piece. A transaction uses whole pieces and sends the difference back to the owner as a new piece called change. The Unspent output distribution note tells you how a balance is split across its pieces, because that decides how much a future spend will show.
What the note says
- Info
The whole balance is one output. A partial spend of it creates a change output visible on the chain.
- Info
91% of the balance sits in one output. A partial spend of it creates a change output visible on the chain.
- Info
The largest output holds 75% of the balance.
- Good
The balance is spread across several unspent outputs. The largest holds 40%.
What it means
Say an address holds one piece of 1 bitcoin and pays 0.1 bitcoin. The transaction spends the whole piece: 0.1 goes to the recipient, a small fee goes to the miner, and about 0.9 comes back as change. Both amounts are public. Wallets usually send the change to a fresh address of the same wallet, but anyone who can see which address paid can often tell which of the two outputs is the change, and so roughly what was left. When a balance sits in one big piece, a partial spend can show the change this way; the chain alone does not prove who controls a change output. When it is spread across pieces of different sizes, a spend can use a piece close to the amount and show less.
What it does not mean
Change is not a cost and not a loss. It returns to the wallet that paid, in a new piece. The note is not a risk to the funds and not advice to split or merge anything. It describes what the chain would show.
What you can do
If you watch the address, the note explains why a spend from it may change the balance by more than the amount sent, and where the rest went. Whoever controls the address can choose which pieces a transaction spends in wallets that offer coin control.
Common questions
Where does the change go?
Usually to a new address that belongs to the same wallet. That is why a single address rarely shows a whole wallet. See why one address is not a whole wallet.
Why did the balance drop by more than was sent?
The spend used a whole piece. The amount sent and the fee left; the change came back to another address of the same wallet, so this address shows less.
Is a change output an unspent output?
Yes. Once its transaction is confirmed, the change is one more piece the receiving address holds. See what an unspent output is.