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Hi! Based on your experience, how long does it take to receive one confirmation for any given transaction which has payed the standard miner's fee? Is it still reversible?


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If a merchant or trader will be accepting payment on 0 confirmations (or even one or two confirmations), then there is a recommended configuration to lessen the risk of being defrauded due to a race attack. –  Stephen Gornick Jan 31 '13 at 2:51

2 Answers 2

up vote 4 down vote accepted

A Bitcoin transaction, by design, will get one confirmation after an average of 10 minutes. Even before a confirmation has been received, a transaction is generally irreversible.

If you were to send a second (double-spend) transaction, using the same inputs as a transaction you've previously sent, I suppose there might be some custom-developed nodes that would give it priority if the transaction fee was higher than the first transaction. However, I believe most nodes would reject the second transaction.

If one of these (corrupt?) custom-developed nodes was to solve a block including the second transaction, my understanding is that the network would accept the block and thus accept the second transaction. This question has been asked separately, here: Does any pool accept higher-fee transactions of a double spend, instead of the earlier one?

However, it's worth mentioning that standard nodes will not relay the second transaction.

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However you could deliver at the same time two different transactions to two different standard nodes. –  Lohoris Jan 28 '13 at 16:02
This is incorrect. The average target time of 10 minutes means that the average waiting time for a single confirmation is 5 minutes. –  runeks Sep 5 '14 at 17:02
@runeks, you're wrong. There's an explanation here from one of the core Bitcoin developers: bitcointalk.org/index.php?topic=5521.0 –  Highly Irregular Sep 6 '14 at 0:16
@HighlyIrregular I think you are misinterpreting that post. It's physically impossible for the mean time between two generations to be ~600 seconds, and the average duration -- from any random point in time -- to the next generation to be equal. Think about it this way: if a bus departs every 10 minutes, and you arrive at the bus stop at a random time, what's the average amount of time you have to wait? 5 minutes. Remember, the average time between two generations, and the average waiting period until the next generation are two different figures. –  runeks Sep 6 '14 at 11:02
@runeks, Bitcoin block solutions follow a Poisson process, so your example is not appropriate. See this question for an explanation: bitcoin.stackexchange.com/q/3909/516 "The time until the next event (the next block found in our case) follows the exponential distribution with mean 1/λ, which is 10 minutes. This distribution is memoryless - the amount of time spent waiting for a block has no effect on the amount of time left to wait. When a block is found the expected time until the next block is 10 minutes (which is intuitive), and it is also 10 minutes at any other time." –  Highly Irregular Sep 8 '14 at 8:45

simply looking at this chart tells you that average transaction confirmation time is not 10 minutes (block confirmation is 10min)



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