Mining fees are at your expense. These fees are put in place to guarantee the security of the network as well as remunerate miners. These fees may vary depending on the network used as well as how much stress the network is currently under.
When you transfer the entirety of your wallet to an external address, the amount received will be slightly lower due to these mining fees.
If you send part of your wallet to an external address, you will receive the entirety of said amount as the mining fees will be deducted from your Coinhouse wallet.
For more information regarding how fees are fixed, please take a look at our Terms & Conditions.