This guide explains what Coin Control is, why it's useful, and how to use it in the BitBoxApp to manage your Bitcoin transactions.

What is Coin Control?

Coin Control is an advanced feature in the BitBoxApp that lets you manually choose which "pieces" of Bitcoin—known as Unspent Transaction Outputs (UTXOs)—are used when you send a transaction. Normally, the app automatically selects these for you. Coin Control gives you precise power over your on-chain activity for greater privacy and management.

Why use Coin Control?

Using Coin Control offers several powerful advantages for managing your Bitcoin effectively. While standard wallets focus on simplicity, Coin Control empowers you to manage your digital footprint with precision.

Key benefits include:

• Enhance privacy: This is a primary benefit. By selecting which UTXOs to spend, you can avoid linking funds from different sources, such as keeping UTXOs from a KYC exchange separate from those acquired privately. This makes it much harder to trace your transaction history on the public blockchain.
• Perform a Satoshi Test: To prove ownership of a specific address to an exchange, you must send a tiny amount from its associated UTXO. Coin Control is essential for selecting that specific UTXO.
• Consolidate "dust": You can combine many small UTXOs ("dust") into a single, larger one. This simplifies wallet management and can help reduce future transaction fees.
• Manage for tax purposes: Select specific UTXOs based on their purchase date or cost basis to manage capital gains or losses. For example, in some countries, you can spend younger UTXOs to preserve older ones that may qualify for more favorable tax treatment.
• Isolate funds: Keep specific UTXOs separate for budgeting or tracking purposes. For instance, you can use a UTXO received as a gift to pay for a particular item, keeping it separate from your general spending funds.
• Optimize network fees: You can influence a transaction's size (and therefore its fee) by selecting specific UTXOs. Choosing one large UTXO instead of many small ones can result in a smaller transaction size and a lower fee.

How to activate Coin Control

Activating the feature is a simple, one-time step in the BitBoxApp settings.

1. Open the BitBoxApp on your computer.
2. Navigate to Settings in the left sidebar (the gear icon).

3. Click on the Advanced settings tab.

4. Find the Enable coin control option and toggle the switch to the ON position.

How to use Coin Control

Once enabled, the Coin Control panel is available every time you send Bitcoin.

Access the Coin Control panel

1. From the main screen, select your Bitcoin account and click Send.

2. On the Send Bitcoin screen, you will see a button labeled Toggle coin control. 

3. Click this button to open a list of all available UTXOs in your account.

Select your UTXOs

The panel shows each UTXO's amount and its associated address. UTXOs from internal "change addresses" and re-used addresses are also clearly marked. To make identifying UTXOs easier, we highly recommend labeling your transactions.

Simply click on one or more UTXOs from the list to select them as the inputs for your transaction. The BitBoxApp will use their combined value to cover the send amount and the network fee. 

Best practice: Label your transactions

We highly recommend labeling your transactions and addresses, especially if you use Coin Control regularly. Labels add essential context, transforming a list of complex addresses into a clear overview of your funds and their origins. This practice significantly reduces the risk of selecting incorrect UTXOs. For more details, read our guide on managing wallet labels.

Understanding the 'Send selected coins' button

It is important to understand how this function behaves when Coin Control is active.

• Without Coin Control: The button will likely appear as "Send all," and clicking it creates a transaction to spend your entire account balance.

• With Coin Control: If you have manually selected specific UTXOs, clicking Send selected coins will only send the sum of those selected UTXOs (minus the transaction fee). It will not automatically include any other UTXOs in your account.

• When sending a specific amount: If you enter a specific amount to send, the BitBoxApp will use your selected UTXOs to cover that amount plus the network fee. If the total value of your selected UTXOs is greater than the amount you are sending, the remainder will be returned to you as "change" at a new change address to protect your privacy.