Charging for shared utilites

[George Kupsky]

Just bought my 1st rental Jan 2nd. Not yet rented.
Single home with 2 units. 3R 1BA up and a Studio 1BA down.  My son will live in downstairs in July (5 months time)..  Do I pay utilities (last yr avg for elec, gas, sewer/water was approx $325/month) and build a similar amt into rent?  No separate meters as of today. What about when the downstairs is occupied ? (A split of that monthly amt by a % of sq ft  proration?)  Thanks for any input!