Divide it my .13 and that is the maximum price I want to pay for it.  

Personally, I'm just looking for great properties, and if I use NOI (past or future expected) divided by purchase price (past, asking, or likely future, or offer price) then, well, that's just one of my data points that helps guide me.

Your total debt is divided by your income for a ratio called Debt to Income Ratio or DTI.

One of the biggest downfalls with the way I did it was that I did not install in on every wall dividing the units.

I have a 10 bed apartment, which is divided up into 2 units, and have also owned SFR student houses, so can offer some experience also.  

Now we just use actual days and life has been much easier.For full months, which comprise the majority the duration for most loans, we divide the interest rate by 12 and multiply by the principal balance for that month.

Example: Renovation was $10,000 you feel it's acceptable to get paid back in 5 years - $2000/year divided by 12 = $166/mo increase. or round it up $170-$200/mo...Does that make sense?

Let them be part of the motivation.Everyone is either a divider, subtracter, adder, or multiplier. 

My guess is that you would need to bill each expense for each company separately, and expenses that were shared may be divided according to their share of cost or billed all to one, and none to the others.

Washer/Dryer in upstairs unit only. 5 star rated home, walls 18" thick.Summer months:Electric between $250-$350/monthFuel between $100-$150/month (60-100 gallons) when turned on, some months we just turn the boiler off (JUN-AUG)Water/Sewer free except septic maintenance. so far this has been $0 total, but I expect to maybe get it pumped just in case late this year (rough guess $300)Winter months:Electric between $350-$450 monthFuel varies greatly with temp, heaviest usage months, I've purchased 300 gallons per month at the extremes of -40 and below temps.Water/Sewer still no monthly actual cost, but I plan on about $25/month to save for annual maint.When I average out my fuel costs simply taking fuel expeditures divided by 12 months, I get approx. $200/month.