When transferring bitcoin, one may encounter a situation when the coins get stuck and do not reach the receiver in time. Unconfirmed transactions are placed in the bitcoin mempool. Currently, there are 48,000 pending transactions.
The bitcoin network's maximum capacity is seven transactions per second. The higher the load on the network, the more unconfirmed transactions. Confirmation time depends heavily on the transaction fee set by the sender. The higher fee, the faster the miners include the transaction in the block. Consequently, transaction fees increase, and more pending "cheap" transactions occur.
To avoid such scenario, one could use the website called BitcoinFees. Transactions that are most likely to go through first are shown in green.
For better understanding, scroll down to the "Which fee should I use?" section at the bottom of the page. It shows the fastest and cheapest transaction fee.
As of this writing, the optimal fee equals 54,250 satoshis or approximately $6.
What do I do in case the transaction has stuck after all?
Wallets that enable their users to export private keys offer several ways to push the transaction:
CPFP (Child Pays for Parent). Child transaction replaces the parent transaction in the queue for confirmation. This method works as follows: once the payment is sent (and is not yet confirmed), the change is transferred to the sender’s change address. This amount should be sent to the main wallet but now with a higher fee. Miners choose not only transactions with the highest rewards but also groups of transactions sent by a single person if the total transaction fee satisfies them.
Replace-By-Fee. What we are doing here is adding a new fee to the transaction that already exists. When creating a new transaction, the wallet adds a commentary indicating the right to adjust the fee once the payment is put in the queue. For instance, the Electrum wallet has two options—“Edit fees manually” and “Replace-By-Fee”:
Before sending the coins, make sure to enable the "Replaceable" option:
If the transaction does not get confirmed for a long time, one could try raising the transaction fee. All they need to do is go to the wallet history, choose the pending transaction, and set a new, additional fee:
Double spending. A manual version of Opt-In Replace-By-Fee. A user has to manually create the second transaction so that the network does not consider it a mistake and does not cancel it. This is an outdated way to push the transaction, and it is hardly necessary as wallets such as Bitcoin Core, Green Address, and Electrum already support Replace-By-Fee.
Accelerators. This is the easiest way to push your transaction. There are many pools like ViaBTC. They help users speed up the transactions by assigning priorities. The pool aims to include the transactions with the lowest fees in the block first, thereby decreasing the network’s congestion. To use this method, one needs to get the transaction ID from Blockchain.info. Copy the wallet address to this window:
Then look for the same string as on the screenshot:
And copy it to this window:
The service offers up to 100 free speed-ups an hour. If during this time the transaction is not included in the block, one should send the request again. For special cases, such as transactions with extremely low fees or those that need to go through urgently, the service offers paid services.
The same could be achieved with the help of ConfirmTX. The website partnered with several pools and claims to speed up the transaction in 72 hours. If the transaction weighs over 250 bytes, a user will need to pay $5. All other transactions are processed free of charge.
If none of the methods worked for you or they are not supported by the wallet of your choice, just be patient until the system itself cancels the transaction. Transactions in the mempool can wait up to 14 days to get confirmed. Once that time is over, unconfirmed bitcoin gets back to the sender’s wallet.