Definition
Child-Pays-For-Parent, or CPFP, is a fee-bumping technique that lets the receiver of funds, not just the sender, speed up a slow transaction. The recipient creates a new child transaction that spends an output of the stuck, low-fee parent and attaches a high fee to that child. Because the two are economically linked, miners are incentivized to confirm them as a pair.
How miners evaluate the package
Bitcoin's consensus rules require that the transaction creating an output appear in the chain before the transaction spending it. Miners exploit this by assessing transactions as a package: they look at the combined fee and combined size of the parent and child together. If the parent's fee alone is too low but the child contributes a large fee, the total package feerate becomes attractive, and a miner pulls both into a block at once.
When to reach for CPFP
CPFP is most useful when you are receiving funds in a transaction someone else broadcast with a fee that turned out to be too low, since you cannot edit their transaction. It is also handy when a wallet does not support replacing the original. The trade-off is that the child must itself pay enough to lift the whole package above the prevailing market feerate, so it can cost more than simply replacing the parent would have.
CPFP is the recipient-side counterpart to Replace-By-Fee (RBF), which the sender uses instead. Both ultimately influence which transactions a miner selects when assembling the next block.
In Simple Terms
Child-Pays-For-Parent, or CPFP, is a fee-bumping technique that lets the receiver of funds, not just the sender, speed up a slow transaction. The recipient creates…