Capital gains tax, page-13

General advice:
Include brokerage costs to the cost base of each transaction eg if you buy $5000 of a share and pay 19.95 brokerage the cost base is 5019.95. When you sell subtract the brokerage on that transaction and your gain is smaller by the brokerage amounts.

As for prior year losses they can be used for current year gains as long as you haven't applied them in previous years. You can carry fwd any unused losses in your tax return for record keeping, but keep good records.