Confirmation (Transactions)

In blockchains, a confirmation is the inclusion of a transaction in a block that has been added to the chain. Once that happens, the transaction has one confirmation; each additional block built on top adds another. Before its first confirmation, a transaction waits in the mempool and can still be replaced or dropped. Each confirmation makes it harder to reverse, because undoing it would require a chain reorganization replacing all the blocks since. On Bitcoin, where a block arrives roughly every ten minutes, services often treat six confirmations as final, while chains with formal finality reach it after set checkpoints. The topic is covered in more depth under Transaction Confirmations. Also see Zero Confirmation Transaction.