Confirmation

A confirmation happens when a transaction is included in a block and added to the blockchain; each additional block built on top counts as another confirmation. More confirmations make a transaction harder to reverse, because rewriting history would mean redoing all the work or stake behind those blocks. Different services require different numbers of confirmations before treating a payment as final.

A common misconception is that one confirmation is always enough; for larger amounts, more confirmations reduce the small remaining risk of reversal. See how a crypto transaction gets confirmed.