What is the mempool? Where crypto transactions wait to be confirmed
By SendPay Business · · 2 min read
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The mempool, short for memory pool, is the waiting room for transactions that have been sent but not yet added to a block. Each node on the network keeps its own mempool, and miners pick transactions from it to build the next block.
How transactions leave the mempool
- You send a transaction and nodes pass it around the network.
- It sits in the mempool, marked as unconfirmed.
- Miners choose which transactions to include, usually the ones paying the highest fee for their size.
- Once included in a block, it has its first confirmation.
Why some payments wait longer
Bitcoin adds a new block roughly every 10 minutes and each block has limited space. When many people send at once, the mempool fills up, fees rise and low-fee transactions can wait hours or longer.
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If a payment gets stuck
Some wallets let you raise the fee on a waiting transaction, known as replace-by-fee, or send a follow-on transaction that pays a higher fee to pull both through. Very old unconfirmed transactions may eventually drop out of most mempools.
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Questions people ask
How long until my deposit confirms?
Work out the wait for the confirmations an app needs, network by network.
Confirmation time calculator →What will my Bitcoin transaction cost?
Estimate its size and fee at any fee rate, free.
Bitcoin fee calculator →What is a pending transaction?
A payment that has started but hasn't fully gone through yet.
Pending transactions →Read next
Spotted a mistake or something out of date? and we'll fix it. How our guides are made
This guide is general information, not legal or financial advice. SendPay Business is a technology company, not a bank, and does not take deposits; regulated services on the platforms are provided by licensed partners. Other companies named in this guide are reference points only and are not affiliated with SendPay Business.