Hi - I have a rental property that was rented out for the fully year of 2019. However, there were 3 months that my tenant paid rent late in the following year in 2020 so I won't report those 3 months rental income until I file 2020 returns next year. However for calculating the fair rental use days would I still use 365 days since my tenant was living in this unit for the full 2019 but a few months rent was paid late in 2020?
When the rent was paid is completely irrelevant. The property was rented "the whole year". Every single day of it. Period. End of story. Even if the renter stopped paying rent in say, Oct of 2019 and you ended up evicting them in say Jan of 2020, it does not change the fact the property was rented the entire year. The only "fact" that changes is the amount of rental income actually received in 2019, and that's it.