Sending a transaction does not put it straight into the ledger. Your wallet signs it and passes it to a <a href="/glossary/node/">node</a>, which checks that it is well formed and properly funded, then relays it to its peers. Within seconds most of the network is holding a copy in memory. Nothing has happened yet in an accounting sense; the transaction is a candidate, not a fact, until it lands in a <a href="/glossary/block/">block</a>.
Block space is limited, so whoever builds the next block chooses which waiting transactions to include, and they generally choose the ones paying the most per unit of space. That is the whole reason fees float. On a quiet network almost everything clears at the minimum, while during a rush the queue grows and the price of getting in quickly climbs. A transaction offering too little may sit for a long time, and nodes eventually drop stale entries from their pools altogether.
There is no single, official mempool. Because each node keeps its own view, two mempool explorers can disagree slightly about what is pending. This also has a privacy consequence worth understanding: an unconfirmed transaction is publicly visible before it settles, so anyone watching can see what you intend to do and react first. If a payment is stuck, most wallets offer a fee bump or a replacement rather than a cancellation, and it helps to check current conditions before sending. Our walkthrough on <a href="/toolkit/how-to-estimate-a-network-fee/">estimating a network fee</a> covers how to read the queue.
Key takeaways
- A transaction in the mempool is broadcast but not settled, and it can still be replaced, dropped or reordered.
- Fees float because block builders pick the highest-paying transactions from a queue with limited space.
- Every node keeps its own mempool, so pending-transaction views differ slightly between explorers and wallets.
Mempool — frequently asked questions
My transaction has been pending for hours. What can I do?
First check whether the network is simply busy, since a low fee in a crowded queue may just need patience. Most wallets support a fee bump, sometimes labelled replace-by-fee or speed-up, which rebroadcasts the same transaction at a higher fee. If your chain does not support that, some transactions eventually expire from mempools and the funds become spendable again. Never send a second payment assuming the first has failed.
Can anyone see my transaction before it confirms?
Yes. Once broadcast, it sits in public mempools where anyone running a node can read the addresses and amounts involved. On chains with automated traders this visibility can be used to place transactions ahead of yours in the same block, which is one reason a swap sometimes fills at a worse price than quoted. Assume anything you broadcast is public immediately.
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