Bitcoin Forum

So, last night I took an offline wallet, stuck it in the Bitcoin data directory, fired up Bitcoin.exe, sent some coins, and immediately shut down the client.  This morning I realize that the coins never actually went anywhere (confirmed by both the client and Block Explorer).

My question is this: when you send coins using the standard client, how long do you have to wait before it's safe to shut down the client?  Until it shows up in Block Explorer?  Until the client shows the transaction as confirmed?  Both?

It depends how sure you need to be. What probably happened in your case is that the client never actually sent the transaction anywhere or the transaction was forced to be so extremely low priority it never got anywhere (you may have handed it only to peers who refused to pass it on). As soon as a normal priority transaction hits the network, assuming it is not part of an intentionally attempted double-spend, it should be confirmed eventually even if the client does nothing.

When it shows up in Block Explorer, does that mean it's "for sure"?

Technically no, but for practical purposes, almost always yes. If you assume the sender is not doing something nefarious and the transaction is not absurdly low priority, then yes for all practical purposes. If you are the recipient of a transfer of a large number of bitcoins, you may wish to wait for a few more blocks.

All of this confirmation is needed only to protect against double spends. If you're the sender, then you know you're not double spending.

It's just me, sending from one wallet to another, so there is no counterparty risk or anything like that.

Then you can be 99.995% sure it will get confirmed eventually. Since it was in a block, it's obviously been broadcast. Even if that block gets invalidated, eventually some miner who is willing to include your transaction will get a block. Since there's no counter-party risk, that's good enough.

Thanks for your help Joel.