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Inputs and outputs – Bitcoin “change” explained

Did you ever try to send out Bitcoins and found out that a larger amount than what you intended seemed to be sent ? Here’s an explanation why this happens…

The blockchain is a big file that keeps track of all Bitcoin transactions ever made. So if you own some Bitcoins, all it means is that the blockchain has references to transactions that were made to your Bitcoin address. The term for these references is “Inputs”.

Now let’s say you enter a store to buy a watch for 1 Bitcoin. instead of taking out actual cash from your pocket and paying for something you just tell the seller – “here are the references that I have this money” or “here are my inputs”.

What you mean is – here are previous transactions sent to me that add up to 1 Bitcoin or more. This is called an output, so each output is compiled out of 1 or more previous inputs.

Once you use an input to pay for something it is considered “spent” and you can’t use it again for other outputs. So in this case once your output is confirmed it will become an input for the seller to use in future transactions.

Bitcoin rules state that you can’t use just a part of an input. So if for example I wanted to send the seller 1 Bitcoin and the only input or reference I have is from someone who previously sent me 1.5 Bitcoins I will have to use all of this input and return the “change” back to my original address as a new input. So I will use my 1.5 Bitcoins input, pay 1 Bitcoin to the seller, pay a miner’s fee and return the rest to my original address.

Now for a real live example – if you examine the inputs closely you will see that the output consists of an input of 0.142 Bitcoins. 0.005 Bitcoins were sent to someone else, a miner’s fee of 0.0001 Bitcoins was deducted and the rest of the money was sent back to the original address.

That’s why you’ll sometimes see additional coins sent with your transactions. These coins will be sent back to your change address which you can configure manually inside your wallet.

If you want to inquire more on specific inputs you can enable “advanced” mode in Blockchain, track inputs and see which inputs have been spent or not.

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37 comments on “Inputs and outputs – Bitcoin “change” explained”

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  1. Hi I am new to this, I have a transaction with unspent coin with over 50k confirmations, I understand that my outputs are my unspent and in order to spent I need to use as an input in another transaction, Question what are the next steps I need to take to spend my unspent coins,

  2. Hello, about 3 days ago i made a transaction, and the person who i sent the btcs to said that they still have not received yet. in my wallet the transaction says it is confirmed, and i have checked the transaction on the block chain, which says the ‘7 Inputs Consumed and “5 Outputs Created” If anyone knows what this means, or why the transaction has taken long to be received, please let me know. any information would be highly appreciated.
    Warm regards,
    Thanks.

    1. Hi Robert,

      Well, I wouldn’t worry about the inputs and outputs at this stage. Do you have the transaction ID (txID)? Your wallet should give you the txID in the details of the transaction. When you have it, it’s easy to search for the txID in any block explorer – such as https://blockstream.info/nojs/ – and that will confirm whether the amount reached a certain address or not.

      If the block explorer shows that the amount was sent to the intended address, then that’s what happened, without any shadow of doubt.

      If you send me the txID and intended address I can check it, but you should be able to see for yourself if the transaction went through or not.

  3. I sent btc to my mining mangers wallet (Antpoolmininginternational) for investment is there anyway i can check the status of my bitcoin investment. I have the wallet ID. I looked it up on bitcoin explorer and it is there but I dont understand how to read the transaction Or have i been scammed cos now they want $967usd before i can get profits $4600 Please advise

    1. Steven Hay (staff)

      Hi Dannstarrr,

      I’m afraid that sounds like an absolute scam, yes. It’s common for scammers to dangle large rewards which are only accessible if you send money. If you do so, they’ll have some new charge for you to pay.

  4. Hi Sophia,

    Please give me the transaction ID so I can check it out, I may be able to offer some further assistance then.

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