How can i determine if any amount of my estimated payment for 2018 remains when IRS used my payments towards joint return of 2013;currently shows tax record not owing ?

You can go on the IRS website and View Your Balance and Payment History. Click here.

On IRS website shows nothing owed...would it show a credit if i filed an extension?
I did not deduct the amounts paid to IRS in 2018 for my 2017 taxes...is that correct then to put nothing for extension payments?