Can't Get Numbers to Work

[Mark Beekman]

I've been reading, analyzing, and wracking my brain to come up with a set plan of action for rental buying, but the numbers just don't seem to work.

I've been taking the gross rental income and subtracting about 5% for vacancies. I then subtract 15% of that number to allow for a property management firm's service. I then estimate that 60% of that number will be my net income (allowing for taxes, maintenance, etc.). My mortage is always near or slightly higher than my net income. Am I doing something wrong? Should I be making low-ball offers on the properties to make it work? Am I grossly over-estimating the costs and expenses?