The total balance and available balance of the selected asset is shown by the account menu on the top right-hand side of the interface. The total balance is the amount available to withdraw plus any balance used as margin for open positions plus the PnL. The available balance is the amount available for withdrawal or new positions.
You can click on the account menu to display your balances for each asset (BTC, ETH and USDT) and the total USD equivalent. Once expanded, the account menu will also display an overview of the sub-accounts and their respective balances for the selected asset:
The total and available balances of all assets are also displayed by the browser panel, along with the total USD equivalent:
You can also view and manage your balances from this page: https://app.interdax.com/app/wallets/balances.
As shown above, by navigating to this page you can transfer funds between sub-accounts, make deposits/withdrawals, or view your available balance, total balance, initial margin, maintenance margin and hold for each asset.