Return on Investment question

[Stephen Palmer]

Currently my rent is about $1500 a month for my apartment. I am looking to buy a Multi, and I am trying to understand fundamental concepts and definitions. If I move into the first floor, renting out the second with the idea that the tenant pays most of the mortgage. If I am left with a $300 payment after the tenants rent, am I technically making $1200 cash flow since I drastically decreased my cost of living each month?