Realistic cash flow numbers

[Adi P.]

I have 7 rental properties. I have been calculating my expected cash flow the way most of you probably do. rents less all expenses, including a certain % for possible vacancies and maintenance.  My maintenance has tended to be higher than expected. So even though I actually went through and calculated an average maintenance cost/year based on the real numbers over all the years I've had each property, I still never actually get that much income. 

Today I realized one mistake - I had been subtracting average maintenance and possible vacancies from Net rents instead of Gross. I went through today and changed it, but then my total predicted income is MUCH less than I actually make. Because of course (and happily) I don't lose that money on all properties every year - maybe only 2/7. 

My question for you folks - if you have multiple properties, how do you tend to estimate your income? 

Somehow add something back or decrease the % off for vacancies. etc? Or some other way? 

Thanks for any ideas.