What are good assumptions to determine monthly expenses?

[Henry Le]

Hello fellow investors,

There are expenses that come with single-family rentals.  What are some estimates you use to determine your net rent after expenses?

I live in Sacramento.  So far, my expenses include the following:

- Property Taxes: 1.25% of purchase price

- Rental Insurance: 0.5% of purchase price

- Management Fees: 10% of gross rent

- Vacancy Rate: 10% of gross rent

- Repairs & Capex: 10% of gross rent

- Utilities: (garbage, sewer, water): 10% of gross rent

- Mortgage: 30 year with 20% down payment

With these assumption, I get negative cash flow in my area.  I applied the parameters to other areas such as Memphis, Nashville, Cleveland, etc. and the cash flow is barely positive.  

I see people saying they achieve north of 15% cash on cash returns.  Is it because their assumptions are different than what I have?

Thanks.