Bitcoin Forum

So i use bitcoin-qt on windows.
Lets say i send a coin to somebody - how do i know which of my various adresses was used?

Probably none of them.  Why does it matter?

Bitcoin doesn't spend "from addresses".  It spends discrete unspent outputs.

Your wallet knows that certain previously unspent outputs are now spent, and knows about any new unspent outputs that it has the ability to spend.

Saying that you are sending bitcoins "from" and address or "to" and address is just terminology that we humans use to make it easier to discuss the transfer of control over value.  In reality in the technical details there aren't any bitcoins, and these non-existent things don't "come from" anywhere or "go to" anywhere.

Instead a ledger is updated that encumbers a value with a requirement.  Anyone that can satisfy that requirement is allowed by all peers on the network to apply that value to a new ledger entry that and encumbers it with new requirements.  Notice, there is nothing in that description about sending to or from anywhere.

Go to blockchain.info and enter the address which you sent coins to. You will see which address the transaction came from.

So I have a bank account in which I've deposited $100 in $20 notes.
Let's say I write a cheque for $20 - How do I know which of my various $20 notes was used?

To answer your original question, you don't, and if you think you need to, you're probably doing something wrong.

thanx, so thats only way?
makes way more sense that philosophy above :)

i was *thinking* to test this 'famous' double your bitcoin on .onion and they need it
but now when i see replies. i assume this stuff is pure scam and i shouldnt riks even pennies with it

You assume correctly.

And now you're catching on.

What's wrong with going on blockchain with the transaction ID?