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23 votes
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Why is there "Change" in Bitcoins?

Bitcoin follows a Unspent Transaction Output (utxo) model. Our modern banking systems follow an account model - you're assigned a bank account number (similar to an address), and send and receive ...
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  • 16.5k
18 votes
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If bitcoin is indivisible, where does change come from?

I like to suggest a mental model where the network is a metals forge: You have a 1 oz gold coin stamped with your key on it, with your transaction you send it to the forge to be melted down and re-...
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  • 7,519
17 votes
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Can a Bitcoin transaction have the same address for input and output?

At the protocol level, there is no such thing as "balance of an address". There are individual unspent outputs (like coins in a wallet), which must be individually spent. You can't partially spend an ...
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16 votes

What does change address mean inside Electrum wallet?

Receiving addresses are addresses generated specifically for sharing with people to send payments to you. Change addresses are generated by your wallet automatically when you send funds to someone ...
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  • 13.7k
12 votes
Accepted

Why is the change address for a transaction the same as the originator address?

Many wallets let you control where to send the change. In most cases it is advisable to send to a new address to reduce traceability and increase your privacy a little, but not everyone does and ...
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11 votes

Why is there "Change" in Bitcoins?

There are a lot of good answers, but I want to point out the most obvious answer. Say you have 1 bitcoin and you send 0.2 bitcoin to me and the design leaves it so that you still have 0.8 bitcoin in ...
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8 votes

What can be changed in signed bitcoin transaction?

Here is the list of known sources of malleability from BIP62 (which has been withdrawn, and is no longer up to date, but does give some insight): DER encoded ECDSA signatures Right now, the Bitcoin ...
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7 votes

Why does Bitcoin use separate change addresses?

Change is sent to a new address to improve your privacy and the privacy of the other Bitcoin users you interact with. Let's imagine you receive a payment from Alice in one transaction; then you spend ...
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7 votes

If bitcoin is indivisible, where does change come from?

I'm adding this as an additional answer to the ones that exist, to clarify a comment: if the outputs can be split exactly, then why the inputs can't be split so I only spend the exact amount I want....
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6 votes
Accepted

Why are there round numbers after the fees and no change?

If your wallet has a large UTXO pool with some variance in the values, it is often possible to find a combination of inputs that provide a matching amount to pay for recipient output and transaction ...
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  • 64.6k
5 votes

How to find the change / sender address given a txid?

Each transaction can have multiple inputs and thus can have multiple senders. Here's how you get the sender(s): bitcoin-cli getrawtransaction ...
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  • 776
5 votes

Sending bitcoins to same address

You can send bitcoins to the same address you are sending from, if you create a raw transaction manually, or if you use a wallet that does not create a new change address each time a transaction is ...
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  • 1,334
5 votes
Accepted

Why are change addresses not associated with an account in your wallet?

Bitcoin Core's wallet interprets Bitcoin transactions as payments. A payment is sending money from one entity to another, and is independent from what exact coins were sent and how much change was ...
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5 votes

If bitcoin is indivisible, where does change come from?

It's not the value, it's the inputs. If you have 1 input worth 1 BTC and sent Alice .22 BTC as one output and your change would be a 2nd output. A single input can be split into many outputs. If Bob, ...
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  • 5,243
5 votes
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Where is the change from the output stored in?

When a sender creates a transaction, they explicitly define which pieces of bitcoin they spend. We call such pieces of bitcoin Unspent Transaction Outputs (UTXO) and you can think of the UTXO set as ...
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  • 64.6k
5 votes

Why is there "Change" in Bitcoins?

And if so, why don't you just send 0.4 BTC in the beginning? Bitcoin was designed to allow single-in multi-out or multi-in multi-out payments. In Ethereum, only one address fills the whole "to&...
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  • 9,849
4 votes

Why is the change address for a transaction the same as the originator address?

Bitcoin Core sends change to a different address, but the Bitcoin protocol does not require that. You can write a Bitcoin client that sends the change to the original address. There's no benefit to ...
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  • 28.8k
4 votes
Accepted

When a block that has a transaction with change in it is successfully mined, is the change transaction included in the newly mined block?

There is no change transaction type. Transactions are defined as a list of inputs consumed, and outputs created, and the values assigned to those new outputs. The creator typically makes an output ...
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  • 15.1k
4 votes
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Why do transactions send coins to the same address as they spent it from?

Likely the sender didn't have an unspent output that had exactly the amount he wanted to send. So he choose an unspent output that had enough and sent the remainder back to himself. Accounts do not ...
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4 votes

If bitcoin is indivisible, where does change come from?

The bitcoins themselves never really exist, only receipts from previous transactions. So if received that 1 BTC from a friend, you have a receipt somewhere saying that he sent you 1 BTC. You can then ...
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  • 141
4 votes

What happens when two transactions send to the same address?

It works just fine. Bitcoin transactions can have multiple inputs and outputs; each input is a "pointer" to an output of a previous transaction (specifically, it consists of a transaction id and ...
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4 votes

Why is there "Change" in Bitcoins?

There are some good answers here, but I'm surprised nobody has mentioned privacy. Having coins sent to a new change address can improve your privacy in many ways. Consider this simple example: a one-...
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  • 17.4k
3 votes
Accepted

How are change addresses treated differently by Bitcoin Core?

Is the address deleted as soon as the funds it received as change are spent? No, the change address is not deleted but it is stored as another of your key pairs of your wallet. Bassically when you ...
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  • 849
3 votes

Using bitcore to create a transaction with two addresses and change address

I figured this out, the new transaction code should look like this with the address generated using fromString() method using bitcore. var address = bitcore.Address.fromString('...
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3 votes
Accepted

How can I define the change address of a transaction using createrawtransaction?

In Bitcoin, change is a normal output which sends the remaining money to one of your addresses. When creating a transaction with createrawtransaction, you have to add change output manually (just like ...
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3 votes
Accepted

How to find the change / sender address given a txid?

Bitcoin may use multiple outputs from different addresses to fund the transaction. It will always be impossible to predict what the user is doing, for example, they could be using CoinJoin and the ...
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3 votes
Accepted

Why does coinbase make 2 transfers instead of one

When you receive money, a UTXO (unspent transaction output) is generated and assigned to your address. When you want to spend money, you can only ever spend entire UTXOs. However, you may have ...
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  • 3,154
3 votes
Accepted

Anonymity of Bitcoin ownership a fakery?

Bitcoin isn't anonymous in any rigorous sense, and the developers never claimed it was. See for instance https://en.bitcoin.it/wiki/Anonymity. If someone has been telling you that it is, then indeed ...
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3 votes
Accepted

Why did the remaining money go to another address?

What you are observing is a change address. The wallet created a new address for itself to send the change of spending the 1 BTC to. This is so that it is non-obvious to the rest of the world which ...
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3 votes
Accepted

Seemingly random transactions on testnet

Testnet is generally pretty noisy, filled with strange transactions and nonsensical movements of money. I personally hold wallets responsible for 20%+ of all transactions in the block chain, and most ...
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  • 15.1k

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