My Bitcoin transaction is stuck: how do RBF and CPFP work?

Originally, a transaction had to opt in by setting an input's nSequence below 0xfffffffe. Since Bitcoin Core 28.0, nodes accept replacements whether or not the original signalled ("full RBF") by default. Some wallets still refuse to bump a transaction that didn't signal, so enable RBF in your wallet anyway.

If you sent from a Bitcoin Core wallet:

# Bump to 25 sat/vB; the wallet reduces your change output to pay for it
bitcoin-cli -rpcwallet=mywallet -named bumpfee <txid> fee_rate=25

# Watch-only / hardware wallet: get an unsigned PSBT instead
bitcoin-cli -rpcwallet=mywallet -named psbtbumpfee <txid> fee_rate=25

bumpfee returns a new txid. Anything that tracks the old txid (your database, a block explorer link you sent someone) must switch to the new one. The old one will never confirm.

RBF can also redirect the payment. That is exactly why a merchant should never treat an unconfirmed payment as settled.

Child-Pays-For-Parent (CPFP)

If you can't replace the transaction (you're the receiver, or the sender's wallet doesn't support RBF), spend one of its outputs in a new transaction with a high fee. Miners select transactions by ancestor feerate: a child can only be mined together with its unconfirmed parent, so they evaluate the pair as a package:

package feerate = (parent fee + child fee) / (parent vsize + child vsize)

Say the parent is 200 vB and pays 2 sat/vB (400 sats), and you want the package at 20 sat/vB with a 150 vB child:

needed total fee = 20 × (200 + 150) = 7,000 sats
child fee        = 7,000 − 400      = 6,600 sats   (44 sat/vB on its own)

With Bitcoin Core, spend the specific output back to yourself:

bitcoin-cli -rpcwallet=mywallet -named sendall \
  recipients='["bc1q...your-own-address"]' \
  fee_rate=20 \
  options='{"inputs":[{"txid":"<parent_txid>","vout":1}]}'

Recent Bitcoin Core wallets account for low-feerate unconfirmed ancestors when you set fee_rate, so the child should come out large enough to bring the package up to about 20 sat/vB. Always verify rather than assume:

bitcoin-cli getmempoolentry <child_txid>
# compare fees.ancestor / ancestorsize against your target feerate

CPFP limits to know:

• The parent must still be in the mempools miners see. If nodes have already evicted it for low fees, a child alone can't pull it back in. Newer Bitcoin Core versions relay a one-parent-one-child package together, but don't count on every node doing so.
• You need an output you control. A sender can use their change output, and a receiver can use their payment output.
• A child adds bytes, so for the same result CPFP usually costs more than RBF.

RBF vs CPFP

If it's gone from the mempool

An evicted transaction can still confirm if someone rebroadcasts it, so "gone" isn't "cancelled". The only real cancellation is a conflicting transaction that spends the same input at a proper fee and confirms. RBF is exactly that, and it works even after eviction because it's a fresh broadcast. In Bitcoin Core you can also free the inputs with abandontransaction <txid>, which only works once the transaction is out of your node's mempool, and then spend them again. Until the conflicting transaction confirms, the original can still win.

Fixes

1. Check the feerate you paid against estimatesmartfee and against what recent blocks included.
2. As the sender: bumpfee (or psbtbumpfee), then track the new txid.
3. As the receiver, or when RBF isn't available: CPFP from an output you control, and size the child for the package feerate.
4. Confirm the result with getmempoolentry (ancestor fee and size).
5. Build wallets that signal RBF, use current fee estimates, and never treat zero-confirmation payments as final.

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