Calculating ROI on rental propety?

[Kyle Rowe]

What method do you guys use for calculating ROI on rental property? I've been searching around but, almost every method gives me a different rate of return and some use future sales of the property in the equation which in my opinion is not a factor at my age. Along with the method, what is an ideal ROI? And does that factor in for inflation, etc? Is there a rule of thumb as far as making X % more than commercial interest rates?

Thanks all!