Why after filling in the boxes that that reflect what's on the T4 does an amount show in box 26 when it wasn't filled on the T4?

Did you Auto-Fill your return? The amount in box 26 is the amount of CPP/QPP pensionable earnings which were paid on your income.

Thank you for choosing TurboTax.

Hi there

I don’t use auto fill - I enter everything manually from the T4. I’m working on my 18 year olds taxes and there wasn’t any CPP amounts listed only EI.

@pepsi222 If you don't enter anything for box 26 (or Box 24), then TurboTax will automatically calculate the amount. The number is used to see if there is a CPP overpayment, which if one exists, the amount would be refunded or used to reduce your balance owing.