Real Estate taxes noob question

When calculating real estate taxes i paid for 2020 for example is it the transaction date that matters (has to be in 2020) or is it the Tax Year  that matters? for example in 2020 i paid two installments so two payments but one is for Tax Year 2019 and one is for 2020.  For my 2020 return do i use both or just the one for tax year 2020?

thank you