Get your taxes done using TurboTax

Actually, this is not a program error, if you are entering all 3 rooms as separate rentals.

If you tell TurboTax that Rental A is 20% of your home, for instance, and enter the full amount of your home's real estate tax, it correctly calculates 20% as a Rental Expense and puts the other 80% into Itemized Deductions.  

If you do the same for Rental B and Rental C, you will have triple the amount of real estate tax reported on Schedule A.  TurboTax doesn't know that you have 2 other rentals for the same home that you are entering a % of.  

A couple workarounds would be to:

(1) enter the rental portions of the taxes yourself (choose that option as shown on screenshot), and enter the Schedule A amounts yourself.

(2) Combine Rental A, B, and C as one rental, with a total % of your home, and let TurboTax do the calculations.  Then when you enter 40% of your property is rental, for example, you'll get the correct amount for the rental and for Schedule A when you enter the total home taxes. 

Click this link for more discussion on Renting Multiple Rooms in My Home.