Subtract out the taxes then subtract out the total number of reservations x the cleaning fees.

Take your Rent and subtract the PITI + PMI and the reserves and you get your monthly cash flow. 

Takes a couple minutes.Your Name for the Property____Your Purchase Price of the Property (Subtract the Land Costs),____Freestanding, Leasehold Building/Renovation SELECT Freestanding ____ Leasehold Building/Renovation ____ Date Acquired or Placed in Service____Current Tax Year?

Take that number and subtract out the cost of demo.

So if you sold a home for 500,000, they will not subtract the basis from purchase, but will add 500k to your taxable income.

Subtract the hours you expect to sub for mechanical/electrical work.  

I would work with a local market pro to some up with an ARV (as repaired value), then subtract out your profit margin, closing costs, rehab cost, and remember to build in a little reserve for contingencies that pop up That becomes your "strike price" and you will never want to go above that no matter what.

I do have a property manager, and they added up all the repairs, last month of rent, time spend off market fixing the place, and send them a final statement once deposit was subtracted.

With two vacancies and the owners house not rented, and the rentals bringing in $11K, we would be at a 0 or negative cash flow by the time we subtract the HELOC payment.

If I was you I would let the seller know you are intending on buying the house to rehab and flip for a profit and that the deal will only work for you if the property is acquired by you for less than market value, then let them be the first to set a price, then you either accept knowing it is well below market value and at or under your max price you accept if not than you start the negotiation by telling them the most you can spend is X and that includes the rehab costs which you figure to be around X so subtract that from the max you can spend and that is what you can offer the seller.