Confirmation

A confirmation is the inclusion of a transaction in a blockchain block, plus each additional block built on top of it — a count of how deeply the transaction is buried in the chain. A transaction with zero confirmations is still waiting in the mempool; one confirmation means it has been included in a block; six confirmations means five more blocks have been added after it. The more confirmations, the harder it becomes for the transaction to be reversed by a chain reorganization.

Confirmations matter because a blockchain's most recent blocks can occasionally be replaced if the network briefly disagrees on the latest history. Waiting for multiple confirmations makes reversal astronomically unlikely. For example, an exchange might credit a bitcoin deposit after 2 to 6 confirmations — roughly 20 to 60 minutes given Bitcoin's average 10-minute block time — while accepting a small payment after just one. Merchants handling trivial amounts sometimes accept zero-confirmation transactions, trading security for speed.

A common misconception is that a transaction visible in your wallet is final; until it has at least one confirmation it is merely pending, can be delayed indefinitely if the fee is too low, and in some cases can be replaced by the sender. Different chains treat finality differently: proof-of-stake networks like Ethereum reach explicit finality within minutes, after which reversal is protocol-level impossible rather than just improbable, so the traditional confirmation count matters most on proof-of-work chains like Bitcoin.