Replace-by-fee (RBF) and CPFP

Replace-by-fee (RBF) is a Bitcoin feature that lets you replace an unconfirmed transaction with a new version that pays a higher fee. If your transaction is stuck in the mempool because the fee was too low, an RBF "fee bump" gets miners to prioritise it.

Originally, transactions had to signal that they could be replaced. Bitcoin Core version 28, released in 2024, turned on "full RBF" by default, so nodes running it accept replacements even for transactions that did not signal. This means merchants should not treat unconfirmed transactions as final.

CPFP, or child-pays-for-parent, is an alternative fee-bump method. The recipient (or the sender, using a change output) spends the stuck transaction's output in a new transaction with a high fee. Miners who want that fee must include both, so the parent gets confirmed too.

Many wallets, including Electrum, Sparrow and BlueWallet, offer a "bump fee" button that uses one of these methods.