UTXO transactions
Choose example coins and see how inputs become a payment, a fee and change.
A transaction spends whole unspent outputs as inputs and creates new outputs. Selected input value equals the recipient payment plus the fee and any change. Unselected coins stay available.
Practise this concept
The interactive example needs JavaScript. The explanation and worked example are available below.
Worked example
Select 6,000 and 4,000 sats. A 7,000 sat payment with a 500 sat example fee leaves 2,500 sats change. Selecting only 6,000 cannot cover it. With 6,000 + 2,000, a 7,500 sat payment and 500 sat fee leave no change output.
About this model
Arithmetic practice with example coins only. This does not create keys, addresses, signatures or real transactions. The fee is an example, not a fee estimate. Dust and network relay rules are omitted; a zero example fee does not promise network acceptance.