### How long does it take on average to receive one confirmation? Is it still reversible?

• 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?

Thanks!

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.

• 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.

However you could deliver at the same time two different transactions to two different standard nodes.

This is incorrect. The average target time of 10 minutes means that the average waiting time for a single confirmation is 5 minutes.

@runeks, you're wrong. There's an explanation here from one of the core Bitcoin developers: https://bitcointalk.org/index.php?topic=5521.0

@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, Bitcoin block solutions follow a Poisson process, so your example is not appropriate. See this question for an explanation: http://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."*

@runeks Assuming the hashrate is constant and the difficulty exactly matches it, the expected time until the next block is _always_ 10 minutes, regardless of how long you have waited so far.

Cancelling unconfirmed transactions is a new feature of the system rolling out in Feb.