Unfortunately your available balance for new orders isn't displayed on the site. We realize that this is very inconvenient and we're working on adding the available balance, but I don't know when it might be ready.
If you have trades on to buy with EUR (for example), you can go to Funding > Withdraw > EUR and look at your "withheld" amount. Your "withheld" amount is usually the amount you have tied up in open orders, so that number subtracted from your balance in EUR will tell you how much EUR you have left for new orders. If your balance in EUR is less than your verification tier withdrawal limit, then the figure listed as your "maximum withdrawal" amount will be the same as the amount of funds you have left for new orders. The same goes for other currencies - you can look under Funding > Withdraw > [currency] to see how much is withheld in that currency. It's a workaround and not a great one, but it's the best I can tell you at the present time.