Your 'Available to bet' or 'Total available' balance is the amount available for you to wager at any given time.
Your ‘Available to bet’ balance is your account balance, minus the (current) exposure associated with any bets you have placed that have not yet been settled.
Your exposure is the total amount you have used on unsettled bets. You have an exposure limit, which is set as a default of £10000 (or currency equivalent). This can be changed if you're nearing this limit.
When you are logged in, you can view (or hide) your ‘Total available’ balance in the top right corner of the screen. You can also use the refresh button to see an up-to-date figure that reflects newly placed bets.
Your ‘Available to bet’ balance is also displayed on your ‘Account Summary’ in ‘My Account’. You will notice that there is a figure for each of your wallets (‘Main Wallet’, 'Exchange Games Wallet’ and ‘Poker Wallet’), as well as a combined figure at the top of the ‘Account Summary’ under your ‘Username’.
It is possible that you have a "positive exposure" due to guaranteed profits in ‘Express Payout’ markets. In this case your ‘Available to bet’ balance is higher than your actual account balance.