# Confirmation (block confirmation) 1. When a [[Transaction(s)|transaction]] has been confirmed, it means it has been approved by the network and permanently appended to the [[Blockchain|blockchain]]. 2. The concept of ‘confirmation’ comes into play when a [[Transaction(s)|transaction]] has to be added to a particular [[blockchain]]. In this regard, it should be pointed out that different trading platforms require a varying number of confirmations to finalize [[Crypto (cryptocurrency)|cryptocurrency]] transactions. 4. A confirmation means that the [[network]] has verified the [[blockchain]] transaction. This happens through a process known as [[mining]], in a [[Proof of Work (PoW)|Proof of Work]] system (e.g., [[Bitcoin (blockchain)]]). Once a transaction is successfully confirmed it theoretically cannot be reversed or [[Double Spend|double spent]]. The more confirmations a transaction has, the harder it becomes to perform a double spend [[Attack (hack)|attack]]. 3. The determination of how [[immutable]] the information in a [[blockchain]] is. For many [[Consensus Mechanism (algorithm)|consensus]] protocols, chain reorganizations occur (and are expected) during the confirmation process. Different blockchains have different metrics for what [[Block(s)|blocks]] can be considered immutable and therefore confirmed. #### Example If two valid [[Block(s)|blocks]] are submitted for the same [[block height]], one of them will eventually be discarded, while the other one will become the canonical block from which future blocks are built. The highest blocks in a chain are more likely to be reordered or discarded, with a probability that is inversely correlated to their block depth. In some contexts, confirmations refer to the number of [[Node(s)|nodes]] that have accepted a transaction, the number of [[Transaction(s)|transactions]] that reference it, or the number of blocks that are above it. In [[Bitcoin (blockchain)|Bitcoin]], a transaction has five confirmations when five blocks have been produced after the block containing the transaction. 3. A [[Transaction(s)|transaction]] is "confirmed" when it is included in a new [[Block(s)|block]]. Transactions that have not yet been incorporated into blocks are considered unconfirmed. If the transaction belongs to a block, it is considered confirmed. As new blocks are added after the block to which the transaction belongs, it is confirmed further. For transactions with low commissions, it can take time to get included in the block and they may remain unconfirmed for a long time. Confirmed transactions are confirmed even if they are on [[Orphan Block|orphan blocks]]. However, orphan block branches usually grow to only about two blocks, so they only have two confirmations. In general, a transaction is considered almost certainly safe if it has six or more confirmations. However, there have been cases where operators' system failures caused transactions with six authentications to be [[Roll Back|rolled back]], so it is important to choose a secure operator. 4. Confirmation in the world of [[blockchain]] refers to the process of determining the extent of the [[immutability]] of the information in a blockchain. In some cases, confirmations refer to the number of [[Node(s)|nodes]] accepted in a [[Transaction(s)|transaction]], the number of transactions referencing the confirmation, or the number of [[Block(s)|blocks]] prior to it. A general transaction in [[Bitcoin (blockchain)|Bitcoin]] features five confirmations upon producing five blocks after the block containing a specific transaction. 6. A bitcoin [[Transaction(s)|transaction]] is confirmed once it has been included in a [[Block(s)|block]] on the blockchain by a [[Miner(s)|miner]]. Each subsequent [[Block(s)|block]] added to the blockchain is another confirmation for that transaction. 6+ confirmations is generally accepted for a transaction to be finalized although 99.99% of the time [[Bitcoin Cash (BCH)|Bitcoin Cash]] transactions can be considered final with 0 or 1 confirmation. 5. The successful act of [[Hash|hashing]] a transaction and adding it to the [[Blockchain|blockchain]]. All transactions on the blockchain need to be verified by all [[Node(s)|nodes]]. 7. Confirmation means that a transaction has been processed by the network and is highly unlikely to be reversed. [[Transaction(s)|Transactions]] receive a confirmation when they are included in a [[Block(s)|block]] and for each subsequent [[Block(s)|block]]. Even a single confirmation can be considered secure for low value transactions, although for larger amounts like $1,000 USD, it makes sense to wait for 6 [[Confirmation Score]] or more. Each confirmation exponentially decreases the risk of a reversed transaction. 6. A confirmation simply means that the [[blockchain]] transaction has been verified by the network. This happens through a process known as mining, in a [[Proof of Work (PoW)]] system, as in [[Bitcoin (blockchain)|Bitcoin]]. Once a transaction is confirmed, it cannot be reversed or changed. The amount of confirmations in a [[Block(s)|block]] refer to how many blocks have been added on top of that block on the blockchain. Every added block is counted as a confirmation because all [[Node(s)|nodes]] on the network indirectly also verify (validate) the blocks before it again. Hence, if 5 blocks are added on top of a block, that block has 5 confirmations. The more confirmations a block has, the less likely it is to be changed (harder to [[Attack (hack)|attack]]), thus the safer the transaction is.