50% Rule of thumb when Owner Occupies a unit

[Wendy Geiger]

I want to start by purchasing a 4 plex or lot w/ 4 units. I want to live in one and rent 3 units. I calculated my cashflow differently since I'd be getting rent from 3 units rather then 4. However, I would like to know how it has worked for those who have done it and what fromula would you recommend just as a rule of thumb for filtering though properties.