Split property tax and mortgage interest between residence and rental unit?

[Njmurvin]

I have a residence (4000 sq ft) with a guest house (1000 sq ft) on the same property. I live in the residence and rent out the guest house to a 3rd party. Rent includes all utilities.

When I compute rental expenses in TurboTax, I simply allocate 20% of shared expenses (utilities, etc.) to the rental unit based on square footage. In the past, property tax and mortgage interest (which cover the entire property) were fully deductible for me under my regular deductions, so I never listed them separately as rental expenses.  With tax law changes and retirement, I am now using the standard deduction under which I no longer benefit from those deductions.

Can I allocate 20% of my property tax and mortgage interest as rental expenses? If so, should I report the other 80% under the regular deduction so that the total will match what was reported on the 1098?

[RobertB4444]

Yes, that is exactly how you should report it.  You should be able to report all expenses for the house that way.

@Njmurvin