Schedule A, Line 5a really had me stumped too. But I finally figured mine out. This line includes W2 and 1099-R state taxes paid, as you'd expect, but it also includes SOME Estimated Taxes Paid as described below.
Includes - Estimated taxes paid in the current year for a prior year (like 2022 Q4 taxes paid in Jan 2023)
Includes - Estimated taxes paid in the current year for the current year (like 2023 Q1, Q2, and Q3 taxes paid in 2023)
Excludes - Estimated taxes paid for the current year, but paid after the year ends (like 2023 Q4 taxes paid in January 2024)
Hope this helps!
