I then add the above and subtract it from what I think the house is worth after the rehabbing. 

It's assumed that by 18 you finished school, can read, write, add and subtract, and have command over logic.

I suggest you enter the purchase price, plus settlement costs as the present value, enter the UBP as the future value, take the payments and subtract the servicing costs from the payment, enter the term and solve for the interest rate. 

Value the completed project and subtract all the cost to get there including a development/Entrepreneurial profit.  

So, you determine "Goldilocks" market rents, discount it by whatever stable vacancy factor (say 15%), subtract your expenses (any specific $$$/unit or range?)

Then you can take the value and subtract it from your principal balance (if no loan, then it would be the price they quote).

Also subtract the total amount of your fees, including junk fees, such as government recording fees, document preparation, wire transfer fees, etc.

My understanding of the MA laws is:1. last month can be mingled in your accounts, but the 5% interest has to be given2. sec dep can not be mingled in your accounts and the 5% or has to be given.So, instead of trying to figure this out every year (and you have to calculate correctly), I find it easier to open each separate account, then every year have the bank update the account and subtract the original amount and .....the rest goes back to the tenant.This also (in my mind) a much better way to prove to the courts that you gave the right amount and did return it.Note:  another rule is that you are suppose to have the accounts protected from your assets so that no lawsuit can take it. 

I then make additions/subtract ions for material differences.  

Once the roof is clear subtract all the original roofers fluff and tell him he has a job you will save thousands is my guessGood luckJim