Replace-by-Fee (RBF)

Replace-by-Fee (RBF) is a Bitcoin feature that lets the sender replace an unconfirmed transaction with a new version that spends the same coins and pays a higher fee.

Bitcoin transactions wait in the mempool until a miner includes them in a block, and miners prioritize the highest fee rates. If you paid too little and the network got busy, your transaction can sit there for hours. RBF fixes that directly: your wallet signs a replacement with a higher fee rate, nodes swap it in for the original, and miners now see a more attractive bid. The replacement must pay more in total fees than the original and enough extra to cover its own relay cost.

Originally, a transaction had to signal "opt-in RBF" when it was first sent for nodes to accept a replacement. Since Bitcoin Core 28.0, most nodes accept replacements whether or not the original signaled, but wallets differ: many still only show a "bump fee" or "speed up" button for transactions they marked as replaceable. Check your wallet's settings before you send if fee bumping matters to you.

RBF only works for the sender, because only the sender can sign a new version of the transaction. A recipient waiting on a stuck payment has to use Child Pays for Parent (CPFP) instead, which spends the unconfirmed output with a high-fee child transaction so miners take both together.

This matters for swaps because the order cannot proceed until the deposit gets its first network confirmation. Say you send BTC to a Zest deposit address at 3 sat/vB and the next-block rate jumps to 25 sat/vB. If your wallet supports RBF, bumping the fee to around the half-hour estimate gets the deposit moving without sending a second payment. The replacement goes to the same deposit address for the same amount, so the order still recognizes it. If your wallet has no bump option, the Bitcoin transaction accelerator shows how your fee compares to current estimates and can rebroadcast the transaction, though only a higher fee changes how miners rank it.

One caution: never "fix" a stuck deposit by sending the same amount again. If both transactions eventually confirm, you have paid twice.

The same principle exists on account-based chains, where a wallet resubmits a transaction with the same nonce and a higher gas fee.