Bitcoin change send address

Change addresses

When you view your expanded transaction details, you may see addresses under “Received By” called Change Addresses . To understand change addresses, first we’ll need to explain how cryptocurrency transactions work. Then, we’ll get into change addresses and their role in the transaction process.

Every cryptocurrency transaction is made up of at least one input and output. Inputs and outputs are how the breakdown or denomination of cryptocurrency happens as funds are transacted across the network. Inputs are the existing funds you use when sending a transaction. When those funds come out on the receiving end of a transaction, they are now called outputs. From one transaction to the next, each input is the output of a previous transaction.

To explain inputs and outputs a bit more, let’s use a currency like US dollars as an example. Say you buy something for $20 and pay the the seller with a $20 bill. Later that day, the seller who accepted your $20 leaves work to go buy some dinner. He pays the restaurant with the same $20 that you gave him. Going back to your transaction, the $20 was your output and the seller’s input. In the dinner transaction, the $20 was the merchant’s output and the restaurant’s input.

Now, what if your purchase doesn’t cost $20, but it costs $15? Since all you have is one $20 bill, you can’t pay exactly $15, right? In that case, you’d pay with the $20 bill, and the seller will give you a $5 bill as your change.

Switching gears back to cryptocurrency, change plays a similar role like we explained with the $20 used for a $15 purchase. When you use an input that is worth more than the transaction cost, the extra funds are sent back to you as change through a newly generated address (as opposed to you receiving it to the same address you sent from). This is called your change address .

When you send funds, your change addresses are generated by your wallet, but you won’t see separate transactions in your transaction history for receiving your change; it’s included in the original sending transactions as a second output. You can view your change address for any given outgoing transaction by clicking on your transaction history. Then, expand the specific transaction to view extra details.

Of course, there are times when your transaction may not need a change address. If you end up spending the exact balance of an input, then you won’t need change (just like how, if you bought something from a seller for $20, then the seller wouldn’t have to give you change for your $20 bill).

To sum all of this up, change addresses are an aspect of cryptocurrency that allow users to transact using exact amounts, even if the transaction isn’t the total amount of the output being spent. It’s similar to when people transact with cash. If the buyer pays with a $50 bill, but the transaction cost $35, they would receive $15 in change back. In cryptocurrency, the difference between the total amount paid and the total transaction cost is sent back to the user as change using a change address.

Still have questions about change addresses? Let us know by submitting them here.

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Bitcoin address changed – Why my wallet’s BTC address keep changing?

Has your Bitcoin address changed? When sending / receiving Bitcoin or while just checking the account page of your online wallet you might have observed this. The Bitcoin address currently displayed is different from the one you’ve used in the past.

If you are just getting started with Bitcoin then it may seem quite scary and confusing. If you are concerned then you don’t have to be. This is just a security measure provided by your wallet service provider or the exchange. It’s a quite common occurrence and particularly you’ll notice that your Bitcoin address changes when you request a new transaction.

So why does your Bitcoin wallet receiving address change? What happens to your old address? Do they expire or can you still send funds to your previously used Bitcoin address? Before we explain this there is one thing we’d like to clear.

Different Bitcoin address – Should I be worried?

The confusion here is that beginners think of Bitcoin address as an account number. No, the public BTC address should not be used an account number. Instead consider it as a payment tracking number. Will you be using a single tracking number for all your payments? No, right. This is why most of the online wallets such as Coinbase and blockchain.com automatically generates a new address for every new transaction.

Now another confusion is that you think that you only have one address. No, you have a wallet and the wallet generates address for you to receive Bitcoin. Your Bitcoin wallet is capable of managing hundreds of different Bitcoin addresses. So next time if you see your Bitcoin wallet displaying a different address do not panic. You are most probably using HD (Hierarchical Deterministic) wallet and they keep track of all your old and new addresses.

Alright! But what is the primary reason for Bitcoin address to change every time?

Why does your Bitcoin address keep changing?

As we said if you are using Bitcoin address as an account number then you are doing it wrong. You need to understand that Bitcoin transactions are traceable. Meaning they are public and are permanently stored in the blockchain.

If you use the same Bitcoin address to receive funds then it will get easy for anyone to track your payment history. This is why it is advised that whenever you receive a payment you need to use a new address. This way it becomes harder for one to decide that the address being used is yours by verifying it on the block explorer.

Bitcoin wallet has a feature of changing address to ensure that you are being provided with an unique address every time you make a transaction. Not all wallet types, but specifically HD wallets. This is done to protect your privacy and it’s a basic security protocol build into Bitcoin network.

Okay, but what about my previously used Bitcoin address?

What happens to previous address?

HD wallets uses privacy centric method for generating and managing address. All addresses generated in your wallet or online account will remain tied with your wallet forever. Meaning your previously used address remain valid and you can still receive funds to your old address. However for the prior stated privacy reasons it is recommended that you do not re-use the address.

Does the address change happen with all cryptocurrencies?

Not all wallet types and not all cryptocurrencies. Only HD wallets and only cryptocurrencies that are based on Bitcoin such as: Bitcoin cash, Litecoin, Dash, Dogecoin, Ravencoin etc.

Now whenever you are requesting a payment make sure you are not using same old address to improve privacy. Also when sending funds ensure that you are not sending to a wrong address. Hope you won’t panic next time when you see your Bitcoin address changed.

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How does change work in a bitcoin transaction?

It seems that when you send a bitcoin transaction, all the coins in the sending address are spent in that transaction, divided into the amount that you intended to send, and «change», which goes back to you, but at another (newly created) receiving address.

That makes it a bit difficult to track your balance on block explorer (especially since the new receiving address does not seem to be displayed in the Bitcoin client anywhere).

Does it have it have to work like this, or is this a specific implementation detail of the client software?

Also, do you have to wait for change to be confirmed before you can spend it again?

3 Answers 3

First, let’s clarify the difference between accounts and addresses.

«Accounts» are used for the convenience of people to track their funds. This is primarily used to track the source of funds. Since this is just for your tracking, you can move Bitcoins from one account to another just by moving a number from one column to another. No transactions are needed. (This is like when you know you owe your son $25 for allowance, and you have $200 budgeted for groceries.)

«Addresses» are used to receive Bitcoins in transactions. The coins are sent to an address. The client associates each address with an account and adds received funds to that account. This is simply done for convenience to allow people to track indirectly which address funds were sent to. But you can have any number of addresses associated with the same account.

Change comes from the way Bitcoins are spent. To spend a certain number of Bitcoins, you must pull in Bitcoins from transaction outputs to accounts you control. Note that in the spending part, it doesn’t matter what address this is or what account that address is associated with. When you spend Bitcoins from a particular account, that just means you debit that account for the amount you send. It doesn’t mean the funds come from addresses associated with that account. Remember, the association between addresses and accounts is for receiving only, not sending. (Like when you spend money on groceries, it’s not like you have specific bills for groceries. You just have an amount budgeted.)

So when you pull in transaction outputs, you form a pile of Bitcoins big enough for the number you are trying to send. Usually, it won’t be exact since you must claim an entire output. So the excess forms the ‘change’.

Since there is no address associated with sending Bitcoins, there is no particular address the change should be sent to. So, to preserve anonymity, the client creates a new one just to receive the change from this transaction. Since this address isn’t really associated with an account and shouldn’t be used to receive any more Bitcoins (because that would senselessly tell people the same recipient got the coins as got this change) the client does not display it.

Because the client manages coins in a particular way, it doesn’t make sense to try to view coins it is managing with any kind of explorer. It’s specifically trying to obscure the fact that all the coins are related. Those kinds of services are intended to monitor recieved funds, not managed funds.

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What is Bitcoin change address? “Change” output and address explained

Have you just made a Bitcoin payment and discovered that part of your Bitcoins are transferred to an unknown address? Do not worry. Your wallet it not compromised or is neither a bug. They are just send to a change address that you own and is one of the key privacy feature of Bitcoin.

This happens often. Whether it is a QT wallet, electrum wallet or whichever Bitcoin wallet it is. Whenever a person sends some coins from their wallet; a specified amount of coins will be send to the intended recipients Bitcoin address and the remainder amount will be returned back to the senders BTC address. Not to the same address but to the change address that is associated with the spenders Bitcoin wallet.

Most users will not notice this change output until they examine their address on a block explorer. Also for beginners this concept tend to be confusing because their BTC address balance will not be accurate and doesn’t add up to the total balance displayed by their wallet. It is because the total balance displayed by the wallet is the balance of all address which includes both the receiving address as well as the change address.

So now what is change address or change output and how it works? Also why send Bitcoin “change” to different address and why not to the original address which the sender used?

Change address and output explained

In Bitcoin; change output is nothing but the remainder amount or the extra amount of satoshi which the spender used in a transaction but is returned back to the spender itself. It is returned back because they don’t wish to pay anything more than the specified amount. The address to which the change output is returned back is called change address. This change address is usually a new Bitcoin address which the client (Bitcoin wallet) generates for the sender to receive back the difference amount.

So instead of getting the difference back why not pay the exact amount of Bitcoins in first place?

To understand the concept of change address or change output let’s first understand the fundamentals of Bitcoin transaction.

Bitcoin transactions

Fundamentally every Bitcoin transaction consist of three things: A transaction input, output and the amount (BTC) used. The transaction input is the address from which the Bitcoins are sent. The transaction output is the address to where the Bitcoins are sent.

Now blockchain is a huge record of data that keep tracks of all Bitcoin transactions from beginning till now. So basically if you own some Bitcoins; the blockchain will have reference to all the previous transactions that constructed Bitcoin to your address.

Before you can send your Bitcoin to someone they were first send to you from someone else address, right?. The address that send to you is the transaction input and the address that received Bitcoin (your BTC address) is the transaction output.

Now if you wish to send your Bitcoin to another person; the address from which you send BTC will become the transaction input. The other persons BTC address that receives your Bitcoin will become the transaction output. So basically at some point outputs might become inputs depending on if they are being spend or not.

If the outputs are not part of another transaction (not spent) then that is where the coins are actually present and is called Unspent Transaction Output (UTXO).

Alright! Now as you have understood inputs, outputs and UTXOs let’s get into the actual topic that is “Change”. Why and how change outputs are created?

Bitcoin change output

In Bitcoin and basically many other cryptocurrencies the UTXO (Unspent Transaction Output) is indivisible. That is when the output of previous transaction becomes the input of another transaction it needs to be spend in its entirety. It cannot be divided and it is the rule. The Bitcoin protocol only allows you to spend the UTXO in full. This is done primarily for two reasons; security and efficiency.

Therefore, if the output is larger than what the user wish to pay in a transaction; a change output is created and it becomes the new UXTO. Likewise, if the output is smaller than what the user wish to pay then the wallet client picks up several of the users unspent outputs as an input to make up the funds.

Each output is compiled of 1 or more inputs and each inputs can be comprised of 1 or more output. So this brings us to conclusion that Bitcoin can be sent from multiple addresses and to multiple addresses all in a single transaction.

Now let us take a look at the below example to better understand the Bitcoin change address.

Example of Bitcoin “change”

Consider the following example where two parties Bob and Alice involve in a transaction.

Bob has 50 Bitcoins which he bought from an exchange and he received it in single output. Now for some reason Bob wish to send Alice 0.5 BTC. However Bob only have one input of 50 BTC.

Since UTXO are indivisible Bob cannot simply send the 0.5 BTC alone. Instead he is required to spend the entire input. That is he spends the entire 50 Bitcoin in a single transaction creating two new UTXOs. One output of 0.5 BTC goes to the destination address (to Alice) and the other 49.5 BTC returns back to the change address which Bob owns.

Example of multiple inputs:

Here is another example where Alice seem to have accumulated several unspent outputs from different people. Alice’s wallet now contains three unspent outputs valued at 0.5 BTC, 0.1 BTC and 0.2 BTC.

Now this time Alice wish to pay Nancy 0.8 BTC. However she doesn’t have 0.8 BTC in a single unspent output. So she uses multiple outputs to add up the total value.

Understanding “Change” in Bitcoin

Is the concept of Bitcoin change address and output still confusing? Alright! Let us take a look at another example which we practice in our day to day lives.

Bitcoin works similar to the way physical cash works.

Let us assume that you have a $100 bill. You went to a coffee shop and had a coffee worth of $25. Now to pay the $25 will you rip the bill? No

You’ll pay the whole $100 bill to the cashier. The cashier takes $25 for the coffee and returns you back the $75 as change. Now since US Dollar bills have fixed denominations your transaction may look something like this:

Inputs:

• $100 (You paid to the cashier)

Outputs:

• $25 goes to cashier
• $20 change back to you
• $20 change back to you
• $20 change back to you
• $10 change back to you
• $5 change back to you

A transaction worth of $100 has been taken place where $25 was paid to other person and $75 was returned back to you as change.

Note: Did you notice how the change amount is not available in your wallet until the cashier paid it back. Just like that in Bitcoin the change output is not available for you to spend until the transaction gets confirmed.

Now this is exactly how a “change” in Bitcoin works. Except in Bitcoin; the bills are called unspent transaction output (UTXO). Also unlike your physical cash transaction; Bitcoin transaction involves transaction fees.

Here is another instance of real transaction involving transaction fees.

In the above transaction what happened is: Address “1GBXjHxe74s7HPR97PvdxPYdghsphcLAZG” sent a payment of 0.00157800 to address “1GBfXw6BaHdo2nggNedFhKJGBi2Yhurmoc“.

However the total inputs involved was 0.03961452 BTC. After paying the transaction fee of 0.00000582 and a payment of 0.00157800 to the recipient address the change amount of 0.0380307 was returned.

As you can see the change amount is returned to a different address rather than the one which the sender originally used. Anyways the change address is in senders possession.

Now you might wonder how the change address is created?

How are change address created?

In the early days of Bitcoin; users are asked to input the change address manually whenever their transaction involved change output. As you can guess, this lead to so many confusion and users lost Bitcoins in the process. Many users accidentally sent change to the wrong address to which they don’t have control.

Now thanks to all the latest Bitcoin wallets that takes care of creating and managing the change address automatically. Before a transaction is initiated your wallet creates the address and assigns it to receive the change output.

It all happens automatically in the wallet background. And do not worry. Since the change address is created by your wallet; your wallet contains the private key of that address. This allows you to spend the extra coins from the change address again. Only thing is as we said before you need to wait for certain block confirmations.

Bitcoin core, electrum and most other wallets are designed to handle this process very well. And you’ll usually find the change addresses in the address tab.

Now the next question most of you have is: Why not receive Bitcoin “change” back to the same address?

Receiving change to same address degrades privacy

Well you can send the change output to the same address. While sending to same address simplifies accounting it reduces users privacy. As we said earlier in this article change addresses play a key role in improving privacy.

By design every Bitcoin transactions are stored permanently on the blockchain. This system is complete transparent and is viewable by everyone. Anybody can trace or check any transaction anytime and easily understand from where the amount was sent and to whom. By linking personal identities one can easily begin to draw conclusions about the persons financial history. This is something alarming and most do not prefer.

So to preserve anonymity and to make the job of tracing transaction more difficult change outputs are usually send to a newly created change address.

Hope it explains everything about Bitcoin change address and output.

The next time if you sent Bitcoins to someone and if you notice a large amount of BTC are transferred to another address, then do not worry. They are your money and the address you see in the transaction is a change address that you control.

Did you find this article educational? Then you may want to read the following articles which will help you learn Bitcoin more.

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