So, how can I make sure that TT is not assuming that that I rent below FMRV?
The program does not make that assumption. There's a screen with a checkbox on it that you would actually have to check, in order to tell the program you rented below FMV.
You don't say the dates the property was classified as a rental. So let me pick some out of thin air that will equate to "4-6 weeks". I am aware it's only a room, and not the entire property.
On Apr 1 you convert the property (that one room as a percentage of your total floor space) from personal use to rental. Then on Jun 1 you convert the property back to personal use. That's 61 days. During that 61 days you never used the room/property for any personal use. But you did rent it out for 40 days.
Days rented: 40
Days personal use. ZERO.
If there was any personal use between Apr 1 and Jun1, then with 40 days rented, the days of personal use can not possibly exceed 21 days. You are only counting the days the property was classified as a rental. Period.
Now most likely, you did not convert the room/property back to personal use. So that would mean the day count from Apr 1 to Dec 31 is 273. Your days rented would still be 40, and your days of personal use can not possibly exceed 233 (273-40).
If you did not convert the property/room back to personal use on your 2020 tax return, then technically speaking, the property/room is still a rental in 2021.
I say you probably did not convert the property back to personal use on your 2020 return, because it's a bit tricky to do that. I can be done. But it's not very intuitive in the program.
