Owner Occupied - How should I calculate expenses?

[Arthur Banks]

Sorry I clicked Post before I finished the title. Owner Occupied - How should I calculate expenses?

I'm purchasing a 2 unit that I will owner occupy (OO) for the first year. Expected rent $2300 fully rented.

Question is, should I budget as though it will be fully rented or the actual rent for that year? For example: vacancy $230/mo (10% of $2300 fully rented) or $115/mo (10% of $1150 actual rent). When I calculated my numbers before purchase I was looking at about $500-$600 cash flow fully rented (self managed). The rent for one unit would just about cover the mortgage save for about $100. (P.S. I'm not asking about the vacancy rate for my market).

Thanks in advance.