Child Pays For Parent
Child Pays For Parent helps confirm a stuck crypto transaction by attaching a high-fee child transaction to a low-fee parent.
Definition
Child Pays For Parent, often shortened to CPFP, is a fee-bumping method used when an unconfirmed cryptocurrency transaction is stuck because its fee is too low. A second transaction, called the child, spends an output from the first transaction, called the parent. The child pays a higher fee, giving miners a reason to confirm both transactions together.
In mining terms, CPFP matters because miners do not only look at transactions one by one. When one transaction depends on another, they can evaluate the whole package. If the combined fee rate is high enough, a low-fee parent can become worth including in a block.
How It Works
When a user broadcasts a transaction, it enters the mempool, where it waits for miners to include it in a block. Miners usually prioritize transactions that pay the highest transaction fee per unit of block space. If the original transaction pays too little, it may sit unconfirmed during busy periods.
CPFP solves this by creating a child transaction that spends coins from the unconfirmed parent. Because the child cannot be valid unless the parent is confirmed first, a miner who wants the high-fee child must also include the low-fee parent. The miner then compares the combined fee and combined size of the two transactions. If that package fee rate is competitive, both transactions can be mined in the same block.
For example, a parent transaction might pay a very low fee because the sender underestimated network congestion. The recipient, or sometimes the sender if they control a change output, can create a child transaction that pays extra. The child does not erase or replace the parent. It simply adds enough fee pressure to make the parent-child pair attractive to miners.
CPFP is different from Replace By Fee. Replace By Fee creates a new version of the original unconfirmed transaction with a higher fee. CPFP leaves the original transaction in place and adds a dependent transaction below it.
Why It Matters
For users, CPFP is a practical way to rescue a payment that is taking too long to confirm. It can be especially useful when the original sender cannot or will not increase the fee, because the recipient may be able to spend the unconfirmed output and pay the extra fee themselves.
For miners, CPFP improves transaction selection. A transaction that looks unprofitable by itself may become profitable when packaged with its child. Mining software that handles parent-child packages well can collect more fees and use scarce block space more efficiently.
CPFP also shows why the mempool is not a simple first-come, first-served queue. Confirmation depends on fees, dependencies, block limits, and miner policy. As block subsidies decline over time, these fee-market tools become more important to miner revenue and user experience.