Calculating rental yield with a mortgage

[Cecilia Schettino]

Hello! I want to calculate a rental yield when I have a mortgage, however I don't think what i am reading in Google is correct.

I am new in all this...

If my property costs 200K USD - and my mortgage monthly cost is let's say 1000USD most websites says I need to calculate:

Income (rent) - costs (mortgage, maintenance)/cost of the property X 100

However I actually maybe put just 30% of the cost of the property, aren't I calculating it twice? This considerably lower the rental yield?

Any help? thank you so much..