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Mempool

The mempool (memory pool) is the waiting area where each Bitcoin node holds valid transactions that have not yet been confirmed in a block. It matters to buyers because bitcoin sent to your wallet waits there until it is confirmed, and the wait grows when the network is busy or the fee rate is too low.

How does the mempool work?

Each node checks new transactions and keeps valid ones in its own mempool, so there is no single shared mempool. Miners usually fill blocks with the highest fee rates first.

The fee rate is the network fee divided by the transaction’s size, in satoshis per virtual byte (sat/vB). It is one of several crypto fees.

Why do transactions get stuck in the mempool?

A transaction gets stuck when its fee rate is too low for demand. As of September 2026, Bitcoin Core nodes by default drop a transaction after two weeks, or sooner if their mempool fills with higher fee rates. A dropped payment is not lost; the sender keeps the coins.

  • Replace-By-Fee (RBF): the sender replaces it with a higher-fee version.
  • Child-Pays-For-Parent (CPFP): a new transaction spends the unconfirmed coins with a high fee, so miners confirm both.

Lightning Network payments happen off-chain and skip the mempool.

Example: how do you check a transaction?

Paste the TXID (transaction ID) into a block explorer. One bitcoin payment looks like this:

  1. Broadcast. Nodes add it to their mempools; explorers show it as unconfirmed.
  2. Wait. Blocks arrive about every 10 minutes on average, though any one block can come much sooner or later (bitcoin.org, as of September 2026).
  3. First confirmation. A miner adds it to a block, nodes drop it from their mempools, and it has 1 confirmation.

Why does the mempool matter when you buy crypto?

Crypto is delivered to the wallet address you provide. Like any on-chain transfer, a purchase waits in the mempool until confirmed; busy networks mean longer waits. See blockchain delays and confirmations, or buy crypto on Coinmama.

What are the risks and red flags?

  • Unconfirmed is not final. A pending transaction can still be replaced or dropped, so wait for confirmations.
  • Beware of “speed-up” offers. Never share your seed phrase with anyone offering to speed up a payment. See how to protect yourself from fraud.

It is still in the mempool, usually because its fee rate is too low for a busy network. For purchases, see blockchain delays and confirmations.

Yes. Pending Ethereum transactions wait in a transaction pool, often called the mempool, until a validator includes them. A higher gas priority fee (tip) makes inclusion more attractive.

Go deeper: How to send Bitcoin to a wallet, step by step.

Related terms

  • Confirmation A confirmation is the inclusion of a transaction in a block.
  • TXID (Transaction ID) A TXID (transaction ID) is the unique string of letters and numbers that identifies one transaction on a blockchain.
  • Block Explorer A block explorer is a website that lets anyone search a public blockchain and see its blocks, transactions, addresses and balances.
  • Network Fees A network fee is the charge for processing a transaction on a blockchain, based on block space and demand, not on the amount sent.
  • Crypto Fees Explained: Spread, Card & Network Fees Crypto fees are the costs of buying, sending or swapping crypto, from processing fees and spreads to network fees paid to miners or validators.

Go deeper

Sources

  1. Bitcoin Developer Guide: P2P network (memory pool) (accessed )
  2. Bitcoin Developer Guide: Transactions (transaction fees) (accessed )
  3. Bitcoin Optech: Replace-by-fee (RBF) (accessed )