When you invest in an after-tax account, you establish a Cost basis. This is the purchase price of the assets, adjusted for stock splits, dividends, and return of capital distributions. Your institution will offer a variety cost basis methods, and your institution will track your cost basis for you.

Each asset you purchase will have a cost basis, but your institution should also aggregate your cost basis for each account for you as well.

If you select “Specific ID” for your cost basis, you will have a high degree of control of the cost of each share your sell which gives you the ability to manage your gains and losses.

These images from Vanguard are provided to indicate how you might locate your Cost Basis from your financial institution's website.

Pull down to "unrealized gains/losses" to view your current cost basis.

The "Total Cost' represents the cost basis in this account.

Once you've identified the cost basis of your after-tax accounts, take care to enter them in the Planner.