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What is CPFP?
Child pays for parent (CPFP) is a way to speed up a stuck Bitcoin transaction by spending one of its unconfirmed outputs in a new transaction that pays a high fee. Miners weigh the two together, so the new child's fee pays for including its low-fee parent.
What it means for you
CPFP can be used by anyone who controls an output of the stuck transaction, so a recipient can speed up an incoming payment, or a sender can use their own change output. It adds a second transaction's worth of bytes, so the extra fee has to cover both the child and the parent.
How it works
Since version 0.13, Bitcoin Core's mining code selects transactions by fee rate including their unconfirmed ancestors, so a low-fee transaction becomes more likely to be mined once a high-fee transaction spending its outputs is relayed. The child's fee is set so that the combined fee of parent and child, divided by their combined virtual size, reaches the target rate. Unlike replace-by-fee, which swaps the original for a new version paying more, CPFP leaves the original transaction unchanged and adds a new one.
An example
Say a 200-vbyte payment to you is stuck at 2 sat/vB, a 400-sat fee, while blocks are clearing at 10 sat/vB. You spend its output in a 150-vbyte child. Together they are 350 vbytes, needing 3,500 sats in total, so the child pays 3,100 sats.
Sources: Bitcoin Core 0.13.0 release notes (ancestor feerate mining), BIP-141: Segregated Witness (virtual size), BIP-125: Opt-in Full Replace-by-Fee Signaling · checked 4 October 2026
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