Is there some secret formula the banks use to establish their business credit limits? 

Rougher neighborhoods tend to turn over tenants faster, but there is no set formula, just averages.

I still don't understand where the 979% comes from - what are they using for a formula?

If you are putting in mid-level finishes, such as laminate countertops, don't use a comp with high-end finishes such as quartz countertops.Step 5 - What you choose as your target acquisition cost formula depends on your and your business model and is not an industry standard. 

And there is a mathematical formula here - because our LENDING requires it to be this way.  

@David Song Interesting plot.

The reason it applies to your all-in cost, including repairs, is because it is a formula to get a desired return based on ratio of rents to purchase price. 

Based on my formula (8.3% vacancy, 10% repair, 5% CapEx, 10% prop mgmt, plus mortgage/prop tax/insurance and utilizes), I came up with $400+ in monthly cashflow and ~8% CoC ROI.

Hello everyone, in the past few weeks I have been practicing property analyzing, but as a beginner I am facing a small problem with  some calculations (ROI, COCROI.. ) since I was given different formulas from different sources.

Allocating common expenses - you can allocate common expenses based upon a formula of # of bedrooms used or square footage of each unit.