How to calculate 2019 Real Estate Taxes Paid?

Note: The original mortgage is paid off and we pay the Tax Collector directly.

In 2018 we switched from an Annual bill to Quarterly payments to spread the impact to our budget. Plus we receive a slight discount on the total to be paid for switching to an installment plan. However the Quarterly payments do not line up with the calendar year.  Therefore, I won't make the 4th and final payment for Tax Year 2019 until March 2020. So do I take the 4th quarter payment for 2018 made in March 2019 and add it to the three 2019 quarterly payments made in June, Sept, and Dec 2019; respectively, and use that total in the box to enter 2019 Real Estate Taxes Paid? Or do I wait until I make the final payment for the 4th quarter of 2019 in March 2020 and use that total for Real Estate Taxes paid in 2019? For now, I have entered the total tax amount listed on the tax bill but it does reflect the discounted amount, which using 2018 data came to 3.25%.