Okay, so I haven't bought an investment property as of yet, but I'm looking to soon. Either by putting cash from savings down for the 20% or using my HELOC as the down payment. But something that I am very curious about is what's after the first property? I cannot seem to find anything that will explain this to me (no I have not called an accountant or mortgage lender yet). So from what I'm understanding, is after 1-2 years of being a land lord, I can use about 75% of the rental income to offset the DTI, if the property is cashflowing of course. How does this work? I know I'd have to report all income on my taxes and what not, but I've read a lot of articles saying to write everything off that I can? So I guess my question is, if I were to write as much as I could off, would that effect me proving the rental income to help my DTI? I am very confused about this.

Example:

Mortgage Payment PITI: 650

Monthly Rent: 950

Would it be 75% of $11,400? (yearly gross rent) or would it be the based off of 75% Net profit? Would be writing as much off as I can effect the amount I can use as income? 

Thank you guys so much for reading this novel and helping me out on this.