Multi Unit Tax Questions

[Whitney Leighton]

Hi, folks-

I'm working on my 2020 taxes and I have a few questions. Last January (1/10/20) I purchased a 4-plex. I occupied one unit for 7 months of the year (March-October). In 2020, 2 of the units were rented for the entire 355 days I owned the property, 1 unit was rented for 7 months and 1 unit was rented for 3 months (after I moved out of it). 

It is my understanding that when calculating deductions on my Schedule E for this property I will need to prorate the portion of the 4-plex that I did not occupy. If I'm thinking about this correctly, my non-deductible portion of rental expenses would be 1/4 (units) x 7/12 (months) = 0.15. So I could deduct 0.85 of the repairs, mortgage interest and other expenses. Anyone can confirm that I am on the right track?

Also, the tax software I use asks for the days I occupied the unit and the days it was rented at fair market value. Not quite sure how to figure this for a 4-plex. 355 days rented and 214 days occupied by me? Will my answer to this question affect my numbers somehow?

Lastly, am I to manually adjust numbers based on my above ratios as I'm entering numbers for repairs, etc? Multiply each deduction by .85 as I go along? And when it comes to mortgage interest, will it be a red flag if I manually enter a number that is .85 of the value on my 1098 form? 

Any input would really be appreciated. This is a tax issue I haven't personally run into before. 

Thanks!