If I have included a T5008 slip on my return, which details my securities transactions for the year, do I also need to complete the capital gains summary section?

No, you don't need to add this information again in the Capital Gains & Capital Gains Deduction Profile. To do so would be double reporting of them, and you certainly don't want to do that.

You can see your entries by going to Income > T-Slips > T5008 - Securities Transactions. You will then land on the T5008 - Summary page. If you look at your Detailed Tax Summary, your Capital Gains will be shown on Line 12700.

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