Child Pays for Parent (CPFP)

Overview

Meaning and scope

Child Pays for Parent is a fee-bumping technique used in UTXO networks such as Bitcoin. A wallet creates a child transaction spending an output from a low-fee unconfirmed parent and attaches enough fee to make the combined package attractive to miners.

How it works

Miners must include the parent before the child, so they evaluate the package’s aggregate fee rate under mempool and policy limits. CPFP requires a spendable parent output and may fail when package size, ancestor limits, dust, or local relay policy prevents acceptance. Wallets should calculate fees across all relevant ancestors, verify that the child output is controlled, and monitor both transaction IDs. Payment systems must not treat the child as confirmed independently; settlement occurs only when the package is mined into the canonical chain.

Operational checks and limits

Wallet defaults, quoted caps, and minimum protocol charges are different values, so interfaces should label each field and avoid presenting a maximum authorization as the amount ultimately paid. An estimate should identify the fee unit, network, block context, and transaction parameters used to calculate it. CPFP is a Bitcoin fee-bumping approach in which a spending child transaction adds fees that make the parent-child package more attractive for confirmation. Effective behavior depends on mempool and relay policy.

Practical example

A merchant spends an unconfirmed change output with a higher-fee child to incentivize miners to include both transactions.

Distinctions

CPFP adds a dependent transaction; replace-by-fee attempts to replace a prior transaction according to relevant policy.

How to evaluate it

Fee and transaction handling policies can vary across nodes and over time; for Child Pays for Parent (CPFP), evaluate the actual policy of the network and the submitting service instead of assuming that a theoretical transaction strategy will be accepted everywhere. When evaluating Child Pays for Parent (CPFP), a business should keep the original transaction identifiers, replacement or child relationships, fee estimates, and confirmation outcome together so that one obligation is not counted twice. Related concepts: transaction.