I know this is a BCH address, but it's the best example I could find. The same concept holds for BTC, so understanding what's going on is relevant.


What one sees is one transactions with two inputs and two outputs.

  1. How does it happen that there are multiple inputs/outputs in a transaction?
  2. How did 12WsyKG89bxTGWV1iguxPWh6UX2ye1X8hD end up with 208.448 and 18Q43boBRU8Sk57SjSfjgFbjvXhBccBrKq with 18.816 - where in that transactional data does it specify which address gets what from the inputs?

1 Answer 1

  • Multiple outputs are usual, just like e-mail.

  • If one of your friends has sent you 5 BTC, and another friend has sent you 2 BTC, you should combine and spend them if you need to buy something for less than 7 BTC and greater than 5 BTC.

(By the way, do you know what a change is?)

  • There is no "This output gets its value from this input" All input values are summed, then spent.
  • Thank you for the link to Change. I was aware of it, but the link provided a much better explanation. If all inputs are summed, do we assume that all inputs are from the same account holder/entity?
    – EvilJordan
    Commented Mar 18, 2018 at 7:18
  • @EvilJordan No, take a look at SIGHASH_SINGLE. It's how CoinJoin works. For more information: en.bitcoin.it/wiki/CoinJoin
    – MCCCS
    Commented Mar 18, 2018 at 7:37
  • Thanks for walking me through this. I thought I understood how this worked, but it's suddenly become a lot more complex. So, from what I gather, if Bob has 2 BTC and wants to send Alice 1 BTC, somehow Tom, with his 1 BTC he wants to go to Jane can also get in the mix, and a transaction will show two inputs (Bob:2, Tom:1) and three outputs (Alice:1,Bob(change):1,Jane:1). I guess my question is how did Tom's transaction to Jane end up in the mix? Is the software doing that to save on bandwidth?
    – EvilJordan
    Commented Mar 18, 2018 at 7:57
  • @EvilJordan Oops, CoinJoin uses SIGHASH_ALL. If you're looking for how CoinJoin works, here's the answer. bitcoin.stackexchange.com/a/57276/38618
    – MCCCS
    Commented Mar 18, 2018 at 8:33
  • Did you initially bring up CoinJoin because this particular transaction I referenced is using it? Seems like a very niche service.
    – EvilJordan
    Commented Mar 18, 2018 at 17:46

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