TurboTax automatically sums up your CPP contributions from your T4s and calculates the overpayment for you, if applicable. In the link from TurboTax FAQ Canada Pension Plan (CPP) amounts on my tax return?
you will find more related information about CPP over deductions.
You've already started receiving CPP benefits.
If you've started collecting CPP, you don't need to make CPP contributions anymore and should receive any amounts you contributed back for the current tax year.
You indicated that you're CPP exempt.
When you indicate that you're CPP exempt in box 28 of your T4, TurboTax automatically calculates any CPP amounts paid as an overpayment.
To make the election or enter the details of a previous election to stop paying CPP using TurboTax Online or in the EasyStep view, go to Income > T-Slips > T4A(P) Canada Pension Plan Benefits.
On the T4A(P) - Summary screen, you can enter your information about previous elections or choose to stop contributing to CPP. You must say "Yes" to the question - "Did you elect to stop contributing to CPP in a year prior to 2017?" This screen will only appear if you were 65 to 70 years of age.
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