Replace-by-Fee
Replace-by-Fee (RBF) is a Bitcoin protocol feature that allows an unconfirmed transaction to be replaced with a new version that pays a higher fee. It enables users to speed up stuck transactions by increasing the fee incentive for miners.
How It Works
When you send a Bitcoin transaction with too low a fee, it may sit in the mempool for hours or even days without being confirmed. RBF solves this by allowing you to create a new version of the transaction with a higher fee. Miners will prefer the higher-fee version because it is more profitable, effectively replacing the original transaction. The BIP125 standard defines the signaling mechanism — transactions opt-in to replaceability by setting a specific sequence number.
As of Bitcoin Core's full RBF implementation, all unconfirmed transactions are considered potentially replaceable regardless of signaling. This is an important security consideration: you should never accept an unconfirmed transaction as payment, because the sender can always broadcast a replacement that redirects the funds. Wait for at least one confirmation, especially for any amount that matters.
Using RBF effectively requires some fee estimation skill. Start with a reasonable fee rate based on current mempool conditions, and bump it if the transaction does not confirm within your desired timeframe. Most modern wallets (Sparrow, Bitcoin Core, and others) make RBF bumping straightforward — usually a single button click that constructs and broadcasts the replacement transaction automatically.
Key Points
- Allows replacing an unconfirmed transaction with a higher-fee version
- Essential tool for unsticking transactions during high-fee periods
- All unconfirmed transactions should be treated as potentially replaceable
- Never accept unconfirmed transactions as final payment — wait for confirmations
- Most modern wallets support RBF fee bumping with a simple interface