You've sent Bitcoin and nothing is happening. The transaction sits in limbo, unconfirmed, while the recipient waits. This is one of the most common frustrations for new Bitcoin users, and it usually comes down to one thing: the fee you attached was too low when the network was busy. Bitcoin fee bumping is the toolkit that gets you out of that situation.
Why transactions get stuck in the first place
Before bumping a fee makes sense, it helps to understand what the Bitcoin mempool is and why it matters. The mempool is the network's waiting room, a pool of unconfirmed transactions queued up for miners to include in the next block. Miners pick transactions in order of fee rate (satoshis per byte), not time of arrival. If your fee is below the current going rate, your transaction sits at the back of the queue indefinitely.
During periods of high demand, such as bull market spikes or large on-chain activity events, the mempool can back up with tens of thousands of pending transactions. A fee that looked reasonable 30 minutes ago can become inadequate within the hour. Fee bumping exists precisely for this scenario.
The two main fee-bumping methods
There are two widely used approaches: Replace-By-Fee (RBF) and Child-Pays-For-Parent (CPFP). They work differently, and which one you use depends on your wallet and whether you're the sender or the recipient.
Replace-By-Fee (RBF)
RBF lets the sender broadcast a second version of the same transaction, this time with a higher fee. The new version replaces the original in the mempool. Miners pick up the replacement because it pays more. For a practical look at how this mechanism fits into the broader picture of unconfirmed payments, see the article on what a Bitcoin replace-by-fee transaction is.
RBF only works if the original transaction was flagged as replaceable when it was created. Most modern wallets, including many popular mobile wallets, set this flag by default. If your wallet supports RBF, you'll usually see a "boost fee" or "speed up" button on the unconfirmed transaction. Tap it, choose a higher fee, and confirm. The replacement broadcasts immediately.
A few things to keep in mind with RBF:
- The recipient cannot use RBF. Only the sender controls the original transaction.
- Some merchants and exchanges don't accept zero-confirmation RBF transactions as payment, because the transaction can technically be replaced until it confirms.
- The higher fee comes out of the same funds in the original transaction, so the amount received by the recipient stays the same.
Child-Pays-For-Parent (CPFP)
CPFP works differently. Instead of replacing the original transaction, you create a new transaction that spends the unconfirmed output. This new transaction, the "child," attaches a high enough fee that miners are incentivised to confirm both the child and the original "parent" together.
The logic is straightforward: miners can't include the child without also confirming the parent, so they evaluate the combined fee rate of both transactions. If the child's fee is high enough to pull the pair's combined rate above the current threshold, both transactions get confirmed in the next block.
CPFP is available to either the sender or the recipient, as long as one of them has received an unconfirmed output they can spend. If you're waiting on an incoming payment and it's stuck, you can use CPFP from your own wallet to unstick it. That's something RBF can't offer you as a recipient.
How to actually bump a fee in practice
The steps vary slightly by wallet, but the general process is the same.
For RBF: open your wallet, find the unconfirmed transaction, and look for a "bump fee," "accelerate," or "replace" option. Your wallet will show you a revised fee estimate. Accept it, and the replacement transaction broadcasts to the network. The original becomes invalid once the new one confirms.
For CPFP: you need a wallet that supports spending unconfirmed outputs. Not all wallets allow this. If yours does, create a new transaction spending the stuck funds and set a fee high enough to cover both transactions at the target fee rate. Some wallets calculate this automatically when you flag the transaction as a CPFP spend.
If your wallet doesn't support either method natively, a third option is a Bitcoin transaction accelerator service. Several mining pools offer fee acceleration where you submit a transaction ID and pay a separate fee (sometimes in Bitcoin, sometimes via credit card) to have the transaction prioritised. Quality and reliability vary significantly between services, so treat this as a last resort.
Calculating the right fee to use
Bumping to an arbitrarily high fee wastes money. The goal is to match or slightly exceed the current mempool clearing rate. mempool.space is one of the most widely used tools for checking real-time fee rates. It shows the current fee rate in sat/vB (satoshis per virtual byte) for different confirmation speed targets, typically the next block, within 3 blocks, or within 6 blocks.
Check the current "high priority" fee rate when you want fast confirmation, or the "medium priority" rate if you can wait 30 to 60 minutes. Set your bump fee at or slightly above the relevant rate. There's no benefit in paying 5x the market rate just because you're anxious.
When fee bumping isn't possible
Not every stuck transaction can be bumped. If the original transaction did not signal RBF opt-in, and neither party received an unconfirmed output they can spend (making CPFP unavailable), the transaction may simply have to wait. In practice, most wallets signal RBF by default now, so this situation is increasingly rare.
Transactions can also time out and drop from the mempool entirely if they remain unconfirmed for long enough, typically 2 to 3 weeks depending on mempool pressure. When a transaction drops, the funds return to the sender's wallet as if the payment never happened. This is inconvenient but not catastrophic. Understanding how Bitcoin network fees are calculated in the first place is the best way to avoid needing fee bumping at all, particularly during busy market periods.
A note on fee bumping and wallet compatibility
McLeod Pacific Investments helps clients buy and sell Bitcoin through multiple payment methods, and the team regularly fields questions about stuck transactions. The short answer: use a wallet that supports RBF by default, check the mempool before you send during busy periods, and don't panic if a transaction takes longer than usual. Fee bumping is a reliable safety net when you need it.