Unconfirmed transactions: why they get stuck and what users should do
What are unconfirmed transactions?
Before being included in the blockchain, transactions must be confirmed by network node operators who mine and add new blocks to the blockchain — miners or validators.
Unconfirmed transactions are those that have not yet been fully processed by miners or validators and added to a final block. As a rule, recording a transaction on the blockchain requires a certain number of confirmations — this process is called validation.
How unconfirmed transactions work
To better understand what unconfirmed transactions are, it is necessary to understand the entire transaction life cycle, from the moment it is sent to being recorded on the blockchain.
First, the user sends a transaction, or in other words, broadcasts it to the blockchain network. This process is called transaction initiation. To send a transaction, the user needs a private key to sign it. A transaction can be not only the transfer of cryptocurrencies, but also an exchange on the blockchain (swap) or adding cryptocurrency to a liquidity pool of a decentralized (DeFi) protocol.
After the user initiates a transaction, it enters the mempool — a queue of unconfirmed transactions. Transactions remain in the mempool until nodes start processing them.
Miners check each transaction according to several parameters, including:
- Sufficient funds on the sender's address balance;
- Whether the paid fee meets the current network requirements;
- Whether the sender's signature is valid.
Nodes process unconfirmed transactions in queue order, depending on the amount of the fee paid. First of all, nodes will process those unconfirmed transactions for which users paid a higher cost.
It should be noted that if the fee amount is too low, the transaction may remain in the mempool for a long time, especially if the network is heavily congested, as users compete to have their transactions processed earlier.
After a transaction receives a certain number of confirmations from nodes, it will be added to a block and eventually recorded on the blockchain. From this moment, the transaction is considered confirmed and cannot be canceled or changed.
Why can unconfirmed transactions get "stuck" for a long time?
Nodes have not yet processed the transaction.
Before miners or validators begin processing unconfirmed transactions broadcast by a user to the network, they enter the mempool, which can contain thousands of such transactions at once.
If the network is congested, transaction confirmation times may be longer than usual. For example, during heavy congestion on the Bitcoin blockchain, the number of required confirmations can sometimes reach 20 or more.
In addition, as network load increases, the average fee cost increases, which should be taken into account before sending a transaction. The current network fee can be checked using block explorers such as:
- Blockchair;
- OKLink;
- GetBlock;
- Blockchain.com;
- Etherscan, BNBScan, Solscan, Tronscan, TONScan, Arbiscan, Polygonscan, and similar services.
The user paid too small a fee.
If the transaction fee is too low, the confirmation process may take several hours or even days. In this case, the user can resend the same transaction with an increased fee.
The higher the fee amount, the faster the nodes will process the unconfirmed transaction. Unconfirmed transactions can be accelerated using built-in wallet functions and third-party services.
On the Bitcoin network, the problem of slow transactions remains most relevant for outdated, or so-called Legacy, addresses that start with the number 1. Most wallets and crypto exchanges support newer address formats, such as Native SegWit or Bech32 (starting with bc1), which enable faster transactions at lower fees.
Due to an error
Some unconfirmed transactions may fail due to errors on the user's side or on the blockchain. Among the most common causes of errors in unconfirmed transactions are:
- Insufficient gas (in networks based on Proof-of-Stake consensus);
- Errors in smart contracts;
- Bugs in the crypto wallet itself or blockchain malfunctions;
- Mismatch of transaction sequence numbers in EVM networks (the Nonce parameter).
How can unconfirmed transactions be accelerated?
Using special crypto wallet features such as Replace-by-Fee (RBF) or the "Child pays for parent" method in the Electrum wallet, users can cancel unconfirmed transactions or speed them up by increasing the fee.
Unconfirmed transactions can be accelerated by increasing their priority through a higher fee or by sending them through trusted servers; however, these functions are suitable only for experienced users.
Note: previously, the ability to cancel unconfirmed transactions was actively used by scammers during cryptocurrency exchanges, since beginners did not know that it was necessary to wait for a certain number of network confirmations before considering a transaction completed.
Another way to resolve long-lasting unconfirmed transactions is to use second-layer (L2) solutions, such as the Lightning Network for Bitcoin and Polygon, or Arbitrum for Ethereum.
Second-layer solutions allow significantly faster transactions, the cost of which can be less than one cent. This makes L2 protocols the most suitable for fast transfers when users need to avoid long transaction confirmation times.
If a transaction remains unconfirmed for a long time, you can try accelerators (transaction accelerators). Such a tool is also available from BestChange — the PushTX service:
What PushTX from BestChange does:
- Sends an unconfirmed transaction to several well-known network nodes;
- helps speed up confirmation without changing the fee;
- Especially useful if a transaction is "stuck" and remains in the mempool for a long time.
It is essential to understand that an accelerator does not guarantee instant confirmation, but it significantly increases the chances, especially during periods of blockchain congestion.