Then subtract estimated closing costs of maybe a couple thousand dollars for a cheep property or a little more for a more expensive property.

Most loan officers forget to subtract the interest you've already paid.  

I get my rents, expenses, etc and can get a good NOI but I don’t know how much to subtract from that for debt.

ExpensesIf the NOI is $371,094 annually, what needs to be subtracted from this number in order to know what the buyer will actually put in their pocket?

You can look at is as -$700 every month or you can take the cost of finding another form of reasonable living, subtract $700, and that is your real cash flow in this situation.

Determine the ARV, subtract out closing costs and estimated rehab, and you'll reach your purchase price.

Take total rent collected (including market rent for your home) and subtract all expenses. 

Don't forget, when calculating pay back time, take the tax bracket that you are in, and subtract that percentage of cost off the discount points, because if you itemize, then you can deduct that percentage off your costs.

Subtract the $48K from $240,000 and the offer is $192,000. 

Is that a good metric to use in determining a $ amount to subtract expenses from?