What is Replace-by-Fee (RBF)?
A feature that allows a sender to replace an unconfirmed transaction with a new version that includes a higher fee. Useful when a transaction is stuck in the mempool.
Why It Matters
Replace-by-Fee is a practical solution to getting stuck transactions unstuck. If you sent a transaction with a low fee and the mempool is now full, your transaction might stay unconfirmed for hours or days. RBF lets you rebroadcast the same transaction with a higher fee, typically bumping it to the front of the queue. This prevents the frustration of watching your transaction sit unconfirmed while you wait. However, RBF requires planning—you must enable it when sending the original transaction. If RBF is not enabled and your transaction gets stuck with too low a fee, you might need to wait for the mempool to clear before it confirms.
How It Works
To use RBF, when sending a transaction, you mark it as "replaceable." If your transaction ends up in the mempool with a low fee, you can create a new transaction spending the same bitcoin with a higher fee, which invalidates the original transaction. Miners see the higher-fee version and will include that instead. The new transaction must pay a higher absolute fee than the original, and many wallets calculate this automatically as "original fee plus a percentage increase." RBF is validated at the protocol level—miners won't include a lower-fee replacement because the higher fee makes it more attractive to mine.