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When seeing transactions I see that the number of confirmations keeps increasing without any limit.

I wanted to know if there is any time limit on including a already confirmed transaction in a block by a miner. Like transactions not older than a year, etc.

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A "confirmation" is merely how many blocks that are after the confirmed transaction in the blockchain plus the transaction's block itself.

For example, if a transaction is in block 5,000, and there are now 5,005 blocks then that transaction has 6 confirmations.

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  • Can you please elaborate? The same transaction should have been included in those 5 blocks to say that the transaction has 5 confirmations. If suppose, that transaction was included in only 2 blocks after the initial confirmation, then that transaction will have 3 confirmations. Am I right?
    – zak
    Commented Jul 22, 2014 at 14:16
  • @zakir No, a transaction, defined as a spent output, can only appear once in the blockchain. "Confirmation" here doesn't mean what one would expect it to mean. It's jargon for "number of blocks after a transaction's block". It doesn't mean "how many people have said 'yes, it's in here'". It's simply a bad misnomer.
    – user5107
    Commented Jul 22, 2014 at 14:31
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    Actually, "number of blocks after a transaction's block" does mean "how many people have said 'yes, it's in here'". Each block contains a (merkle root) hash of its transactions, and a hash of the previous block. The chain of blocks following a transaction all confirm that the transaction happened, although the transaction is only explicitly included in the one block (this may be what @Cincinnatus meant). There's no way for future blocks to "leave out" (i.e. not say 'yes, it's in here') the transaction unless they try to build a block from the chain before the transaction was ever included.
    – Tim S.
    Commented Jul 22, 2014 at 15:16
  • @TimS. Now, don't go shooting holes through my misclarification of a misnomer. ;)) I meant that a node doesn't simply ask for a yay/nay response from another node if a transaction's block has been properly added to the blockchain, which would be far less secure than getting deeper in a locally confirmed PoW merkle chain, as you say. It surely wouldn't take 60 minutes to get 6 of those.
    – user5107
    Commented Jul 22, 2014 at 15:29
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    Yep, yep...good to clarify that we don't trust an easy, simple yay/nay response, we trust blocks (which is basically a yay/nay, but with a proof of a huge amount of work).
    – Tim S.
    Commented Jul 22, 2014 at 15:36

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