Net versus Gross Rental Income

[Cory Grolman]

I'm new to BiggerPockets and this is my first post, so if this inquiry is in the wrong section or if it's redundant, my apologies. 

I've got 11 rental properties in the Atlanta area with a monthly income of around $17k. But after accounting for taxes, repairs, maintenance, insurance, etc, I'm only netting around 50%. Is this good or bad? What is the "normal" ratio of net/gross that landlords of rental properties expect?