Replace-By-Fee (RBF)
Replace-By-Fee is a Bitcoin protocol feature that replaces an unconfirmed transaction with a new version carrying a higher fee, so it confirms faster.
RBF (BIP 125, 2016) solves a practical problem: if fees spike unexpectedly while your transaction waits in the mempool, it can hang for days. RBF replaces it with a transaction using the same inputs but a higher fee. Bitcoin Core v28+ (2024) made full RBF default, meaning all unconfirmed transactions are technically replaceable. Controversial: zero-confirmation merchants lost their security model.
Example
A user sends 1 BTC with fee 10 sats/vB. Mempool spikes to 50 sats/vB. Without RBF: wait. With RBF: replace with a 60 sats/vB version — confirmation in the next block.
Frequently asked questions
RBF or CPFP?
RBF if you're the sender and the tx isn't confirmed. CPFP (Child-Pays-For-Parent) if you're the recipient or want to speed a self-sent output without replacing the original.
Is RBF safe for zero-conf?
No, which is why it's controversial. Merchants delivering on unconfirmed transactions can be RBF-double-spent. Always wait for 1+ confirmations for non-trivial amounts.
Related terms
Further reading
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