Confirmations
security · blockchain
How many blocks have been added starting with the block that includes a transaction.
1.concept
A transaction has its first confirmation when it is included in a block. Each later block on that chain adds another confirmation. A payment still waiting outside a block has zero confirmations, even if it already appears in your wallet.
2.security
More confirmations reduce the chance that a transaction will be reversed by a chain reorganization. The appropriate number depends on the chain's security, the payment value, the recipient's risk tolerance, and whether instant acceptance is worth the risk.
3.reorgs
Confirmations can decrease if the block containing a transaction is removed in a reorg. Transactions usually return to the mempool if still valid, but they may need to be mined again.
For the difference between waiting and inclusion, read how blockchain congestion builds.
Technical reference: Bitcoin developer guide to the block chain.
Related terms
Block
→A batch of valid transactions added to a blockchain, linked to the previous block by a cryptographic hash.
mining · blockchain · security
Block Height
→The position of a block in a blockchain, counted from the genesis block at height zero.
blockchain
Transaction
→A record submitted to a blockchain to make a payment or another permitted change.
blockchain · technical
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