If you make a State Estimated Tax payment in January that is applied to the Fourth Quarter Tax Payment of the previous year, you would enter that state tax payment on Schedule A (Form 1040) Itemized Deductions for the year the payment was made.

Example: If you made a State Estimated Tax payment on January 15, 2021 to be applied to the Fourth Quarter 2020 taxes, the amount paid on January 15, 2021 would be entered in the 2020 return on Line 5a of Schedule A (Form 1040). This amount would not be entered on Schedule A (Form 1040) in the 2020 return.

Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.