Assuming you use the format "o" for your datetime so you have "2016-07-24T18:47:36Z", there is a very simple way to handle this.
Call DateTime.Parse("2016-07-24T18:47:36Z").ToUniversalTime()
.
What happens when you call DateTime.Parse("2016-07-24T18:47:36Z")
is you get a DateTime
set to the local timezone. So it converts it to the local time.
The ToUniversalTime()
changes it to a UTC DateTime
and converts it back to UTC time.