When your wallet says "sent", the money is not necessarily safe yet. This article explains the difference between a transaction being included, confirmed and finalized, how each chain handles it, and how long to wait before you rely on a payment.
Three stages of a transaction
These words are used in slightly different ways, but the idea is the same.
- Included: the transaction is in a block. It shows on an explorer. This block could still be replaced.
- Confirmed: more blocks have been added on top, so replacing it is harder. Each new block is one more confirmation.
- Finalized: the network guarantees that the block will not be reversed, unless a large part of the system breaks. Not every chain has an explicit finality point.
Think of it like a bank cheque. Handing it over is one thing. Seeing the money in your account is another. Knowing it can no longer bounce is the last step.
Reorgs: why waiting helps
Blockchains are run by many nodes, and sometimes two valid blocks are made at almost the same time. Different parts of the network see different blocks for a short moment. Soon one branch becomes longer or gets more votes, and the other is dropped. This is a reorganization, or reorg.
When your block is dropped, your transaction goes back to the waiting pool and is usually included again in a later block. But a payment you thought was done can briefly disappear. In rare and extreme cases, someone could try to rewrite a longer part of the chain on purpose. The more blocks on top of yours, the more work or stake an attacker would need. That is why waiting for more confirmations makes a payment safer.
Bitcoin
Bitcoin has probabilistic finality. There is no single moment when a payment becomes final. Each confirmation makes a reversal less likely.
A common rule of thumb is 6 confirmations, which is about an hour, because blocks come about every 10 minutes on average. Small payments are often accepted at 1 to 3 confirmations. Larger sums often wait for 6 or more. You can watch blocks arrive on the Bitcoin page. More on fees and timing is in Bitcoin mempool and fees.
Ethereum
Ethereum produces a block in a slot of 12 seconds. 32 slots make an epoch. Validators vote on blocks, and the network can mark a block as justified and then finalized.
Finality takes about two epochs, which is about 13 minutes. After that, undoing the block would require destroying a large amount of staked ETH, so reversal is extremely unlikely. Before that, a transaction included in a block is usually safe for ordinary payments, but a reorg of a recent block is possible. See Ethereum.
Solana
Solana uses commitment levels that you can ask for when you read data:
- Processed: the node has seen the transaction in a block. It could still be dropped.
- Confirmed: a large majority of the stake has voted for the block. It is rarely reversed.
- Finalized: the block is rooted, meaning many further blocks have been built on it, and it cannot be undone.
Solana slots are about 400 milliseconds, so confirmed arrives in seconds and finalized takes noticeably longer, but both are quick compared to Bitcoin. Explorers and wallets usually show the confirmed or finalized state. See Solana.
Layer 2 networks
On rollups such as Arbitrum, Base and Optimism, there are several levels.
- Soft confirmation by the sequencer. The L2 has a component that orders transactions, called the sequencer. When it accepts your transaction, you see it included within a second or two. This is fast, but it relies on the sequencer's promise.
- Posted to Ethereum (L1). The sequencer's batches are posted to Ethereum. Once the batch is in an Ethereum block, the data is public, and anyone can rebuild the L2 state.
- Final after L1 finality. When the Ethereum block holding the batch is finalized, the L2 transaction is as final as Ethereum itself.
The 7-day window is about withdrawals
Optimistic rollups have a challenge window of about 7 days. It is often mixed up with finality, but it is something else. It applies when you withdraw funds from the L2 back to Ethereum using the official bridge. The system waits so that anyone can challenge an invalid claim. Normal use of the L2, such as sending and swapping, does not wait 7 days. Fast bridges and exchanges can shorten the wait for you, at a cost and with their own risks. See rollups: optimistic and zero-knowledge and bridges and their risks.
Why exchanges wait for confirmations
When you deposit crypto to an exchange, it may say it needs a number of confirmations. The exchange wants to avoid crediting money that could disappear in a reorg and then be spent or withdrawn. The required number depends on the chain, the risk and the amount. The count is usually higher on chains with probabilistic finality, such as Bitcoin, than on chains with fast explicit finality.
If you wait for a deposit, you can follow the number of confirmations yourself. Search the transaction hash in the header search on ChainMonitor and look at the block and status. See how to read a transaction.
Practical guide
| Chain | A reasonable wait for a normal payment |
|---|---|
| Bitcoin | 1 to 3 confirmations for small sums; 6 for larger ones |
| Ethereum and its L2s | A few blocks for small sums; finalized (about 13 minutes) for large ones |
| Solana | Confirmed for small sums; finalized for large ones |
These are guidelines, not rules. The right wait grows with the amount at risk. When in doubt, wait for finality.
Frequently asked questions
How many confirmations are enough for Bitcoin?
Six is the common rule of thumb for larger payments, which takes about an hour. Small payments are often accepted with fewer.
How long until an Ethereum transaction is final?
Finality takes about two epochs, which is around 13 minutes. A transaction is usually safe for small payments much sooner.
Is a transaction on Base final right away?
It is accepted by the sequencer within seconds, which is enough for most daily use. It becomes as final as Ethereum after its batch is posted to Ethereum and that block is finalized.
What is a blockchain reorg?
A reorg happens when the network drops some recent blocks and switches to another valid branch. Transactions in the dropped blocks go back to the waiting pool and are usually included again.
Does the 7-day wait apply to every L2 transaction?
No. It applies to withdrawals from optimistic rollups to Ethereum through the official bridge. Normal L2 transfers do not wait that long.