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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →A zero-confirmation Bitcoin transaction has been broadcast but is not yet included in a block. It is pending, not settled: accepting it before confirmation means accepting the risk that a conflicting transaction may be confirmed instead.
What does zero confirmation mean in Bitcoin?
“Zero confirmations” means a transaction has not yet been recorded in a block. It may have been broadcast and may appear in a wallet or node, but that visibility is not a blockchain confirmation. The Bitcoin Developer Guide describes these as unconfirmed transactions and cautions that they should generally not be trusted without risk analysis: Bitcoin Developer Guide: Payment Processing.
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Nodes keep unconfirmed transactions in their own memory pools, or mempools. A transaction appearing in one node’s mempool reports that node’s current view; it is not a permanent record, and different nodes may see different transactions. The Bitcoin Developer Guide: P2P Network explains the local and non-persistent nature of this state.
Can a zero-confirmation transaction be reversed or replaced?
Before confirmation, a conflicting transaction can spend the same input. Only one of the conflicting spends can be included in the chain. Because transactions travel through an asynchronous network, seeing one version first does not establish that it will be the one miners confirm. Bitcoin Core explains that there is no globally consistent “first” in transaction relay: Bitcoin Core’s Opt-in RBF FAQ.
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How replace-by-fee fits in
Opt-in replace-by-fee (RBF) is a policy that permits a sender to replace a qualifying unconfirmed transaction with a version that pays a higher fee. RBF is one possible way an unconfirmed payment may change, but it is not the only double-spend risk: Bitcoin Core notes that unconfirmed transactions can be double-spent with or without RBF. Replacement and confirmation terminology is also covered in the Bitcoin Developer Guide glossary.
What changes when a transaction gets confirmations?
A transaction receives its first confirmation when it is included in a block. Each later block adds another confirmation, making replacement increasingly difficult. This reduces risk but does not create an absolute guarantee: recent blocks can themselves be replaced. The confirmation progression is described in the Bitcoin Developer Guide.
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| Payment state | What it establishes | Risk and practical meaning |
|---|---|---|
| Zero confirmations | Broadcast or seen by a node, but not included in a block | Conflicting spend and replacement risk remain; a mempool sighting is local and temporary. |
| One or more confirmations | Included in a block, with later blocks adding confirmations | Risk of replacement declines as blocks accumulate, but confirmation is not mathematical finality. |
Is it safe to accept an unconfirmed Bitcoin payment?
There is no single confirmation threshold that fits every payment. The recipient’s decision is a risk policy: consider the amount, how quickly goods or services are released, whether delivery can be reversed, transaction details, and current network and software conditions. Bitcoin Core’s FAQ stresses that risk assessment depends on multiple conditions and can change with them.
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- For a low-value item delivered immediately, a merchant might accept an unconfirmed payment if it deliberately accepts the associated risk.
- For a high-value or irreversible release, waiting for one or more confirmations may be prudent.
These are risk-management examples, not protocol rules or guarantees. The cited guides do not establish a current probability of a successful zero-confirmation double spend or a universal waiting period. A particular wallet, exchange, merchant, or payment processor may also apply its own policy.
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How to describe a zero-confirmation payment accurately
Use terms such as “broadcast,” “seen by this wallet or node,” or “pending confirmation.” Avoid calling it settled, final, or guaranteed. A wallet display can show that a transaction is visible to that wallet; it cannot by itself prove network-wide agreement or block inclusion.
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