Child Pays For Parent (CPFP)
What the Child Pays For Parent (CPFP) method is all about
The “Child-Pays-for-Parent” (CPFP) technique means that you send from your stuck unconfirmed transaction (the “parent”) a second new transaction (the “child”) with a higher fee covering network duties for both transactions. This technique works for UTXO (Unspent Transaction Output) like Bitcoin, Litecoin, Dogecoin, Cash, etc., and Bitcoin forks only.
Miners get profit from reward + network fees from all transactions in the block. It means miners will prefer a more profitable transaction with a small weight to combine into the block with constant size.
The Bitcoin consensus rules require that a transaction that creates an output must appear earlier in the blockchain than a transaction that spends those outputs. It includes having the parent transaction appear earlier in the same block than the child transaction if both are included in the same block.
In this case, the whole chain of unconfirmed transactions will be added to the block. It makes no difference what amount you send. It could be a few hundred satoshi or the entire amount. The only thing that matters is a higher network fee for a new transaction.
A new unconfirmed transaction with a higher network fee is more profitable for miners, and they will take the whole chain with both unconfirmed transactions into a block. That is how it works.
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In practice, it means that:
You have a transaction that has been unconfirmed for a long time because of the low network fee. It is a “parent” transaction. One of the addresses you are sending coins in this transaction has no confirmed funds.
Create a new transaction sending some coins from this address using these UTXO. The amount you send does not matter. The only thing that matters is the network fee. It shall usually be high to cover both transactions’ fees. It will be a so-called “child” transaction.
The “child” pays for the “parent” due to its higher network fee. Miners will take them both. And they will be confirmed.