Confirmation

Overview

What a confirmation counts

A confirmation generally indicates that a transaction has been included in a blockchain block and how deeply it is buried under newer blocks, depending on that chain's terminology. For Bitcoin, inclusion in a block provides an initial confirmation, and subsequent blocks increase the depth of that transaction in the current best chain. Before inclusion, a transfer may be broadcast and visible to network nodes without any block confirmation. That “seen on the network” stage is not the same as “confirmed.”

How the underlying system works

A transaction seen in a mempool is not yet a confirmed blockchain inclusion. After inclusion, a node can report the number of blocks built on the relevant block, but short chain reorganizations can remove or replace recent blocks. Applications choose their own required confirmation threshold based on asset, network, transaction size and business risk.

On proof-of-stake networks such as Ethereum, inclusion and finalization are distinct protocol milestones. It is misleading to apply Bitcoin-style block depth mechanically to every chain. For a payment service, confirmation status is only one input: a transaction must also use the expected asset, amount, destination and successful contract execution before the order can be accepted.

Why more confirmations can matter

Suppose a Bitcoin merchant sees a payment in the mempool. The transaction could be replaced under network policy or never included. Once miners include it in a block, a competing chain history could still eventually replace that block, though the difficulty generally increases as more blocks build on it. A merchant decides how much confidence is sufficient for the value and risk of its order. A cheap digital download might justify a different policy from a large irreversible shipment. There is no universal safe confirmation count for all networks and all transactions.

Different chains use different finality ideas

On proof-of-stake networks, protocol-specific finality or checkpoints may matter more than a simple count of blocks. A transaction may be included, later justified and finally finalized under rules that differ from Bitcoin's probabilistic confirmation model. Wallets and payment providers can also label states differently. Merchants should know exactly which chain events and business policies produce their “Paid” state. Confirmation protects against certain chain-history risks; it does not tell whether the invoice amount or token contract was correct.

Further reading and related concepts

Reference documents: Bitcoin Developer — Block Chain.

Related glossary topics: Transaction Finality, Chain Reorganization, Transaction Hash.