Crypto glossary
Block confirmation
A block confirmation is each new block added on top of the one containing a transaction; more confirmations make reversing that transaction less likely.
When a transaction is first included in a block it has one confirmation. Each block built after it adds another, because rewriting the transaction would require redoing all of those blocks. On proof-of-work chains such as Bitcoin, the cost of a reversal grows with every confirmation.
Services set their own thresholds. Six confirmations, about an hour on Bitcoin, became a common rule for large payments, while many exchanges credit smaller deposits sooner. On proof-of-stake networks like Ethereum, platforms increasingly wait for finality, the point at which the protocol itself makes a block practically irreversible, which takes around 13 minutes there.
A transaction with zero confirmations is still only in the mempool and can be replaced or dropped, so accepting it for anything valuable is risky. Required waits vary by chain and amount, and smaller networks with less hashrate or stake usually need many more confirmations for the same safety.
Example
An exchange requires three Bitcoin confirmations for deposits; a user who sends 0.2 BTC sees it credited roughly 30 minutes after the first block includes it.
