Replace-by-Fee (RBF)
Replace-by-Fee (RBF) is a Bitcoin transaction feature that allows an unconfirmed transaction to be replaced with a new version that pays a higher transaction fee. This mechanism helps users increase confirmation priority when the original fee is too low or network congestion rises unexpectedly.
Replace-by-Fee (RBF) Explained in Simple Terms
Replace-by-Fee Explained in Simple Terms
When a Bitcoin transaction is broadcast, it enters the mempool and waits for miners to include it in a block.
If the transaction fee is competitive, confirmation may happen quickly. However, if network demand increases or the fee was set too low, the transaction can remain unconfirmed for a long time.
RBF provides a solution.
Instead of waiting indefinitely, the sender can create a replacement transaction that spends the same inputs but offers a higher fee. Because miners generally prioritize more profitable transactions, the updated version is more likely to be confirmed sooner.
This makes RBF a useful tool for managing transaction delays.
How Replace-by-Fee (RBF) Works
How Replace-by-Fee Works
RBF relies on Sequence Numbers within transaction inputs to indicate that replacement is permitted.
The process works as follows:
Original Transaction Created A Bitcoin transaction is broadcast with RBF enabled.
Transaction Remains Unconfirmed The fee proves insufficient for current network conditions.
Replacement Transaction Created The sender constructs a new transaction using the same inputs.
Higher Fee Added The replacement transaction offers a larger miner fee.
Network Accepts the New Version Nodes and miners replace the old transaction with the updated one.
The concept can be summarized as:
The new transaction effectively supersedes the original unconfirmed version.
Example of Replace-by-Fee (RBF) in Practice
Example of Replace-by-Fee
Imagine Alice sends 0.2 BTC to Bob.
The transaction includes a fee of only 2 sat/vB. Shortly afterward, network congestion increases and most miners begin prioritizing transactions paying 10 sat/vB or more.
As a result:
Alice's transaction remains stuck in the mempool
confirmation takes much longer than expected
Using a wallet that supports RBF, Alice creates a replacement transaction with a higher fee rate.
Miners now see the new version as more profitable and are far more likely to include it in the next available block.
Why Replace-by-Fee Matters
RBF improves the user experience by giving senders more control over transaction confirmation.
Without RBF, users often had only two options:
wait for confirmation
create complicated workarounds
RBF provides a simple mechanism for adapting to changing network conditions.
It is particularly useful during:
periods of high transaction volume
sudden fee spikes
urgent payments
RBF vs Child-Pays-for-Parent (CPFP)
Replace-by-Fee (RBF)
The sender creates a replacement version of the original transaction with a higher fee.
Used when:
the sender still controls the transaction
the transaction remains unconfirmed
Child-Pays-for-Parent (CPFP)
A new transaction spends an unconfirmed output and includes a high fee.
Used when:
the recipient wants to accelerate confirmation
the original sender cannot modify the transaction
Both methods help speed up confirmation, but they work differently.
RBF and Mempools
Bitcoin nodes maintain a mempool containing unconfirmed transactions.
When an RBF transaction is broadcast:
nodes compare it to the original
fee requirements are checked
the higher-fee version may replace the previous entry
This replacement process happens before either transaction is confirmed in a block.
Once confirmation occurs, replacement is no longer possible.
Is RBF Safe?
RBF is a standard feature supported by many Bitcoin wallets and nodes.
However, because an unconfirmed transaction can be replaced, merchants sometimes avoid treating zero-confirmation payments as final.
For this reason:
small transactions may be accepted immediately
larger payments often require one or more confirmations
The security of confirmed transactions remains unchanged.
RBF and Bitcoin Wallets
Many modern wallets support RBF by default or offer it as an optional setting.
When enabled, users gain the ability to:
increase fees later
respond to congestion
reduce confirmation uncertainty
Most wallets handle the technical details automatically, making RBF accessible even to beginners.
Related Bitcoin Terms
Sequence Number
Mempool
Transaction Fee
Child-Pays-for-Parent (CPFP)
Locktime
Bitcoin Transaction