I have a client who rented out his second home in 2024 for 80 days to unrelated third parties. He also used it personally for 3 days last year.

Since the rental income was short term in nature (rented for 4.3 days per customer on avg), I am reporting it on Schedule C and using Form 8829 to allocate mortgage interest, real estate taxes, utilities, etc.

Two questions:

1. Will the allocation be based on 80/365 x all of those expenses above? Or is it 362/365 since technically the home was "available to be rented" the entire year - with the exception of the few days he used it personally? How is the numerator defined (the top number in the fraction)?

2. Can I deduct on Sched A the portion of the mortgage interest and real estate taxes that is not used on Sched C?

Thanks for any feedback.