The mempool is the waiting area where valid transactions sit until a miner or validator includes them in a block. A transaction gets stuck there when its fee is too low for the current demand: block space is limited, and transactions that pay more go first. Your coins are not lost. They are in a queue.
On Bitcoin you can move up the queue with RBF or CPFP, and on Ethereum by replacing the transaction with a higher gas price. If the stuck transaction is the deposit for a swap on the SwapRocket exchange, the swap waits for it and continues once the deposit confirms.
- Most stuck transactions are valid and simply paid too low a fee for the congestion at that moment.
- On Bitcoin, use RBF (Replace-By-Fee) or CPFP (Child-Pays-For-Parent).
- On Ethereum, replace the transaction using the same nonce and a higher gas price.
- On fast chains such as Solana, "stuck" usually means the transaction was not broadcast properly or has expired, and you resend it.
- Sometimes the cheapest fix is to wait.
The mempool explained
Picture the security line at an airport. Your boarding pass is valid and your bag is fine, but when the line is long you still wait. The mempool, short for "memory pool", is that line: the set of unconfirmed transactions each node is holding before they go into a block.
Three things follow from that:
- Blocks are limited. Each one holds only so much transaction data.
- Demand changes constantly. When many people transact at once, the line grows.
- Higher fees go first. Fees are the incentive for miners and validators, so they fill blocks with the best-paying transactions.
"The network is congested" means the mempool is full and your fee is not competitive right now.
What your wallet is telling you
- Pending or unconfirmed: the transaction has been broadcast and is waiting in the mempool.
- 0 confirmations: the network has seen it, but it is not in a block yet.
- Dropped: nodes have stopped relaying it, which happens when the fee stays far too low for a long time. The coins become spendable again.
Why transactions get stuck
1. The fee was too low for the traffic
You can send a Bitcoin transaction with a very low fee rate and nothing stops you. When the mempool is crowded, miners take the transactions paying several times more, and yours waits.
2. The fee market changed after you sent
You paid a reasonable fee, and then a rush arrived: a sharp market move, an airdrop claim window, a popular token launch. Fees jumped and your transaction fell down the queue.
3. The wallet's estimate was off
A fee estimate is a forecast. Some wallets lean toward cheap and underestimate how quickly conditions change. On Ethereum this shows when the base fee rises above the maximum your transaction allows.
4. Larger players pay more, automatically
Exchanges and trading bots adjust their fees programmatically and outbid a manual sender without effort.
5. It never reached the mempool
Sometimes the transaction did not propagate: the wallet's node connection was unreliable, or your internet dropped during the broadcast. On high-throughput chains, "pending" more often means "the broadcast failed" than "a long queue".
How to unstick a transaction
Try these in order.
Step 1: Find out what is happening
Copy the transaction ID (TXID) from your wallet and look it up in a block explorer. Check whether the network has seen it and what fee it pays: the rate in sat/vB on Bitcoin, or the max fee and priority fee on Ethereum. If the explorer cannot find it, the wallet did not broadcast it properly, and resending is the fix.
Step 2: Bitcoin, replace it with RBF
Replace-By-Fee lets you rebroadcast the same transaction with a higher fee. Wallets usually label it "Increase fee", "Bump fee" or "Speed up". The extra fee comes out of your change or your wallet balance. The full walkthrough is in RBF and transaction acceleration.
Step 3: Bitcoin without RBF, use CPFP
Child-Pays-For-Parent means spending the unconfirmed output in a new transaction that carries a high fee. Miners evaluate the two as a package, so the combined fee pulls both into a block. CPFP works when you control an output of the stuck transaction: your change, or the payment itself if you are the receiver.
Step 4: Ethereum, replace it with the same nonce
Every Ethereum transaction from an account has a sequence number called a nonce. If you send a new transaction with the same nonce and a higher gas price, the network takes the new one. Wallets offer two buttons for this:
- Speed up: resend the same transaction with more gas.
- Cancel: send a zero-value transaction to yourself with the same nonce and more gas.
The replacement has to pay noticeably more than the original. Nodes generally ignore a bump of less than about a tenth.
Step 5: Be careful with accelerators
Third-party accelerator services claim to prioritise or rebroadcast your transaction. Some are real, and many do little more than rebroadcast. Never share a seed phrase, avoid any that ask you to connect a wallet, and check that the service is built for your chain. For most people RBF, CPFP or a nonce replacement is safer and enough.
Step 6: Or simply wait
If the fee is only slightly low and the congestion is temporary, waiting costs nothing. If the transaction is time-sensitive, use the tools above instead.
Your options at a glance
| Method | Works on | When to use it | Advantage | Drawback |
|---|---|---|---|---|
| Wait | Most chains | The fee is only a little low | No extra cost | Can take hours or longer |
| RBF | Bitcoin | Your wallet supports fee bumping | Clean and reliable | Needs wallet support |
| CPFP | Bitcoin | You control an unconfirmed output | Works without RBF | Slightly more complex |
| Same-nonce replacement | Ethereum and EVM chains | Gas price too low | Built into most wallets | The new fee must be clearly higher |
| Accelerator | Mostly Bitcoin | Poor propagation | Can help visibility | Quality varies, scams exist |
Bitcoin vs Ethereum vs Solana: what "stuck" means on each
Bitcoin: a visible fee queue
Bitcoin has an open fee market, and public explorers show how deep the queue is. Transactions stall when the fee rate is too low or when the mempool swells during volatile periods. The fixes are RBF, CPFP or patience. A transaction that never confirms is eventually dropped by nodes, by default after about two weeks, and the coins become spendable again.
Ethereum: gas and nonces
Ethereum processes each account's transactions in nonce order, so one underpriced transaction blocks every later one from the same account. Stalls come from a base fee that has risen above your maximum, a priority fee that is too low, or nonce conflicts between two devices using the same wallet. The fix is to speed up or cancel with the same nonce.
Solana and other fast chains: usually not a queue
Solana has no long-lived public mempool. A transaction references a recent blockhash and expires within a minute or two if it is not processed. "Pending" there usually means the broadcast failed or the transaction has expired. The fix is to resend it, sometimes after switching the wallet's RPC endpoint or updating the wallet.
Why this matters for swaps
A stuck transaction is more than an annoyance when it is the deposit for a swap.
Take ETH to USDT as an example. You send the ETH with a gas price that is too low and it sits unconfirmed for most of an hour. The swap cannot start until the deposit confirms. SwapRocket uses a floating rate, so the swap executes at the market rate at that later moment, and if ETH has fallen in the meantime you receive less USDT than the estimate you saw. A fee saving of a few cents can cost far more in price movement.
So for a swap deposit, use the wallet's normal or fast setting. The usual timing is covered in how long crypto swaps take, and the pair pages for this example are the ETH to USDT exchange and the BTC to USDT exchange.
How to avoid stuck transactions
Do not default to the slow fee setting. It is fine until the network gets busy. For anything time-sensitive, a slightly higher fee is cheap insurance.
Send when the network is quiet, if you can wait. Fees climb around major news, sharp price moves and popular token launches, and fall back afterwards.
Use a Bitcoin wallet that supports fee bumping. Being able to raise the fee later means a low first guess is not a problem.
Know every layer of cost in a swap. There is the network fee on your deposit, and the service's fee and spread inside the rate. On a DEX there is also gas for token approvals. Crypto swap fees and their hidden costs breaks them down.
Check the network, above all for stablecoins. Many "stuck" deposits were sent on the wrong network, for example USDT on Ethereum when the swap expected Tron. That is not a delay. The swap never sees the deposit, and recovery is not always possible. See the USDT networks guide.
What to do if your swap is waiting on a deposit
If the swap page still shows that it is waiting for your deposit, the cause is one of three things: the deposit is still unconfirmed, it is confirmed but needs more confirmations, or it was sent as the wrong coin or on the wrong network.
- Look up the TXID in a block explorer.
- If it is unconfirmed, bump the fee with RBF or CPFP on Bitcoin, or use "Speed up" on Ethereum.
- If it is confirmed, give it time to reach the required confirmations.
- If the coin or network was wrong, or a confirmed deposit shows no progress for a long time, email support@swaprocket.io with the swap ID and the TXID.
Do not send a second deposit to "fix" the first. More detail is in how to fix a pending or failed swap and the FAQ.
FAQ
Will a pending transaction eventually go through?
Usually, yes, once fees fall to the level it paid. If the fee is far too low for a long time, nodes drop the transaction, the coins become spendable again and you can resend with a better fee.
Can I lose funds because a transaction is pending?
No. A pending transaction has not moved anything yet. The coins are tied up until it either confirms or is dropped, and anything time-sensitive that depends on it is delayed.
Why does one pending Ethereum transaction block the others?
Ethereum processes each account's transactions in nonce order. Until the stuck nonce is confirmed or replaced, later transactions from the same account cannot be included.
Is paying a higher fee always worth it?
No. For a small, non-urgent transfer, waiting is the sensible choice. For a swap deposit or anything with a deadline, a higher fee usually costs less than the delay.
How long can a Bitcoin transaction stay unconfirmed?
As long as its fee is below what miners are accepting. With default settings, nodes discard an unconfirmed transaction after about two weeks, although it can be rebroadcast.
Related reading
- RBF and transaction acceleration for faster swaps
- Crypto swap stuck? How to fix a pending or failed swap
- How long crypto swaps take
When your transaction is moving again and you are ready to exchange, start on the SwapRocket exchange or check the estimate on a pair page such as the BTC to ETH exchange before you send.
