Technical Definition

Child pays for parent (CPFP)

Child pays for parent is a Bitcoin fee-bumping technique where a high-fee child transaction incentivizes miners to confirm it together with its low-fee unconfirmed parent.

By Crypto University Editorial
Replace by fee (RBF)UTXOsat/vB

✦ Key Insight

CPFP can help when a transaction cannot conveniently be replaced through RBF but one of its outputs is spendable.

✕ Common Misconceptions

CPFP requires control of a suitable output and may be more expensive than ordinary fee bumping.

Detailed Explanation

A Bitcoin transaction can spend an output from another transaction even while the earlier transaction is unconfirmed. By giving the new child transaction a sufficiently high fee, the combined package can become attractive to miners.

In Practice

“A wallet receives an unconfirmed Bitcoin payment with a low fee and spends that incoming output using a much higher fee.”

Dig Deeper

Mempool

A mempool is a node's temporary pool of valid, unconfirmed transactions waiting to be included in a block.

sat/vB

sat/vB means satoshis per virtual byte and is a common unit for expressing the fee rate of a Bitcoin transaction.

UTXO

A UTXO is an unspent transaction output that represents a discrete amount of cryptocurrency available to be used as an input in a future transaction.

Replace by fee (RBF)

Replace by fee is a Bitcoin transaction replacement mechanism that can allow an unconfirmed transaction to be replaced by another version offering a higher fee.